From a424a34b8faddf97b5af41689087e7a230f79ba7 Mon Sep 17 00:00:00 2001 From: Raul E Rangel Date: Mon, 9 Feb 2026 13:58:18 -0700 Subject: [PATCH 01/13] serial: 8250: Fix TX deadlock when using DMA `dmaengine_terminate_async` does not guarantee that the `__dma_tx_complete` callback will run. The callback is currently the only place where `dma->tx_running` gets cleared. If the transaction is canceled and the callback never runs, then `dma->tx_running` will never get cleared and we will never schedule new TX DMA transactions again. This change makes it so we clear `dma->tx_running` after we terminate the DMA transaction. This is "safe" because `serial8250_tx_dma_flush` is holding the UART port lock. The first thing the callback does is also grab the UART port lock, so access to `dma->tx_running` is serialized. Fixes: 9e512eaaf8f4 ("serial: 8250: Fix fifo underflow on flush") Cc: stable Signed-off-by: Raul E Rangel Link: https://patch.msgid.link/20260209135815.1.I16366ecb0f62f3c96fe3dd5763fcf6f3c2b4d8cd@changeid Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dma.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c index bdd26c9f34bd..3b6452e759d5 100644 --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -162,7 +162,22 @@ void serial8250_tx_dma_flush(struct uart_8250_port *p) */ dma->tx_size = 0; + /* + * We can't use `dmaengine_terminate_sync` because `uart_flush_buffer` is + * holding the uart port spinlock. + */ dmaengine_terminate_async(dma->txchan); + + /* + * The callback might or might not run. If it doesn't run, we need to ensure + * that `tx_running` is cleared so that we can schedule new transactions. + * If it does run, then the zombie callback will clear `tx_running` again + * and perform a no-op since `tx_size` was cleared above. + * + * In either case, we ASSUME the DMA transaction will terminate before we + * issue a new `serial8250_tx_dma`. + */ + dma->tx_running = 0; } int serial8250_rx_dma(struct uart_8250_port *p) From 24b98e8664e157aff0814a0f49895ee8223f382f Mon Sep 17 00:00:00 2001 From: Peng Zhang Date: Tue, 24 Feb 2026 13:16:39 +0100 Subject: [PATCH 02/13] serial: 8250: always disable IRQ during THRE test commit 039d4926379b ("serial: 8250: Toggle IER bits on only after irq has been set up") moved IRQ setup before the THRE test, in combination with commit 205d300aea75 ("serial: 8250: change lock order in serial8250_do_startup()") the interrupt handler can run during the test and race with its IIR reads. This can produce wrong THRE test results and cause spurious registration of the serial8250_backup_timeout timer. Unconditionally disable the IRQ for the short duration of the test and re-enable it afterwards to avoid the race. Fixes: 039d4926379b ("serial: 8250: Toggle IER bits on only after irq has been set up") Depends-on: 205d300aea75 ("serial: 8250: change lock order in serial8250_do_startup()") Cc: stable Signed-off-by: Peng Zhang Reviewed-by: Muchun Song Signed-off-by: Alban Bedel Tested-by: Maximilian Lueer Link: https://patch.msgid.link/20260224121639.579404-1-alban.bedel@lht.dlh.de Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index cc94af2d578a..a743964c9d22 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2147,8 +2147,7 @@ static void serial8250_THRE_test(struct uart_port *port) if (up->port.flags & UPF_NO_THRE_TEST) return; - if (port->irqflags & IRQF_SHARED) - disable_irq_nosync(port->irq); + disable_irq(port->irq); /* * Test for UARTs that do not reassert THRE when the transmitter is idle and the interrupt @@ -2170,8 +2169,7 @@ static void serial8250_THRE_test(struct uart_port *port) serial_port_out(port, UART_IER, 0); } - if (port->irqflags & IRQF_SHARED) - enable_irq(port->irq); + enable_irq(port->irq); /* * If the interrupt is not reasserted, or we otherwise don't trust the iir, setup a timer to From d54801cd509515f674a5aac1d3ea1401d2a05863 Mon Sep 17 00:00:00 2001 From: Maciej Andrzejewski ICEYE Date: Thu, 5 Mar 2026 13:37:51 +0100 Subject: [PATCH 03/13] serial: uartlite: fix PM runtime usage count underflow on probe ulite_probe() calls pm_runtime_put_autosuspend() at the end of probe without holding a corresponding PM runtime reference for non-console ports. During ulite_assign(), uart_add_one_port() triggers uart_configure_port() which calls ulite_pm() via uart_change_pm(). For non-console ports, the UART core performs a balanced get/put cycle: uart_change_pm(ON) -> ulite_pm() -> pm_runtime_get_sync() +1 uart_change_pm(OFF) -> ulite_pm() -> pm_runtime_put_autosuspend() -1 This leaves no spare reference for the pm_runtime_put_autosuspend() at the end of probe. The PM runtime core prevents the count from actually going below zero, and instead triggers a "Runtime PM usage count underflow!" warning. For console ports the bug is masked: the UART core skips the uart_change_pm(OFF) call, so the UART core's unbalanced get happens to pair with probe's trailing put. Add pm_runtime_get_noresume() before pm_runtime_enable() to take an explicit probe-owned reference that the trailing pm_runtime_put_autosuspend() can release. This ensures a correct usage count regardless of whether the port is a console. Fixes: 5bbe10a6942d ("tty: serial: uartlite: Add runtime pm support") Cc: stable Signed-off-by: Maciej Andrzejewski ICEYE Link: https://patch.msgid.link/20260305123746.4152800-1-maciej.andrzejewski@m-works.net Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/uartlite.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c index 39c1fd1ff9ce..6240c3d4dfd7 100644 --- a/drivers/tty/serial/uartlite.c +++ b/drivers/tty/serial/uartlite.c @@ -878,6 +878,7 @@ of_err: pm_runtime_use_autosuspend(&pdev->dev); pm_runtime_set_autosuspend_delay(&pdev->dev, UART_AUTOSUSPEND_TIMEOUT); pm_runtime_set_active(&pdev->dev); + pm_runtime_get_noresume(&pdev->dev); pm_runtime_enable(&pdev->dev); ret = ulite_assign(&pdev->dev, id, res->start, irq, pdata); From 455ce986fa356ff43a43c0d363ba95fa152f21d5 Mon Sep 17 00:00:00 2001 From: Jiayuan Chen Date: Wed, 4 Feb 2026 15:43:20 +0800 Subject: [PATCH 04/13] serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN uart_write_room() and uart_write() behave inconsistently when xmit_buf is NULL (which happens for PORT_UNKNOWN ports that were never properly initialized): - uart_write_room() returns kfifo_avail() which can be > 0 - uart_write() checks xmit_buf and returns 0 if NULL This inconsistency causes an infinite loop in drivers that rely on tty_write_room() to determine if they can write: while (tty_write_room(tty) > 0) { written = tty->ops->write(...); // written is always 0, loop never exits } For example, caif_serial's handle_tx() enters an infinite loop when used with PORT_UNKNOWN serial ports, causing system hangs. Fix by making uart_write_room() also check xmit_buf and return 0 if it's NULL, consistent with uart_write(). Reproducer: https://gist.github.com/mrpre/d9a694cc0e19828ee3bc3b37983fde13 Signed-off-by: Jiayuan Chen Cc: stable Link: https://patch.msgid.link/20260204074327.226165-1-jiayuan.chen@linux.dev Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/serial_core.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 487756947a96..89cebdd27841 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -643,7 +643,10 @@ static unsigned int uart_write_room(struct tty_struct *tty) unsigned int ret; port = uart_port_ref_lock(state, &flags); - ret = kfifo_avail(&state->port.xmit_fifo); + if (!state->port.xmit_buf) + ret = 0; + else + ret = kfifo_avail(&state->port.xmit_fifo); uart_port_unlock_deref(port, flags); return ret; } From 9c0072bc33d349c83d223e64be30794e11938a6b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Martin=20Roukala=20=28n=C3=A9=20Peres=29?= Date: Mon, 9 Mar 2026 15:53:10 +0200 Subject: [PATCH 05/13] serial: 8250_pci: add support for the AX99100 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This is found in popular brands such as StarTech.com or Delock, and has been a source of frustration to quite a few people, if I can trust Amazon comments complaining about Linux support via the official out-of-the-tree driver. Signed-off-by: Martin Roukala (né Peres) Cc: stable Link: https://patch.msgid.link/20260309-8250_pci_ax99100-v1-1-3328bdfd8e94@mupuf.org Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_pci.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c index aa1ab4da9ff1..6cfd1b2af5b7 100644 --- a/drivers/tty/serial/8250/8250_pci.c +++ b/drivers/tty/serial/8250/8250_pci.c @@ -137,6 +137,8 @@ struct serial_private { }; #define PCI_DEVICE_ID_HPE_PCI_SERIAL 0x37e +#define PCIE_VENDOR_ID_ASIX 0x125B +#define PCIE_DEVICE_ID_AX99100 0x9100 static const struct pci_device_id pci_use_msi[] = { { PCI_DEVICE_SUB(PCI_VENDOR_ID_NETMOS, PCI_DEVICE_ID_NETMOS_9900, @@ -149,6 +151,8 @@ static const struct pci_device_id pci_use_msi[] = { 0xA000, 0x1000) }, { PCI_DEVICE_SUB(PCI_VENDOR_ID_HP_3PAR, PCI_DEVICE_ID_HPE_PCI_SERIAL, PCI_ANY_ID, PCI_ANY_ID) }, + { PCI_DEVICE_SUB(PCIE_VENDOR_ID_ASIX, PCIE_DEVICE_ID_AX99100, + 0xA000, 0x1000) }, { } }; @@ -920,6 +924,7 @@ static int pci_netmos_init(struct pci_dev *dev) case PCI_DEVICE_ID_NETMOS_9912: case PCI_DEVICE_ID_NETMOS_9922: case PCI_DEVICE_ID_NETMOS_9900: + case PCIE_DEVICE_ID_AX99100: num_serial = pci_netmos_9900_numports(dev); break; @@ -2544,6 +2549,14 @@ static struct pci_serial_quirk pci_serial_quirks[] = { .init = pci_netmos_init, .setup = pci_netmos_9900_setup, }, + { + .vendor = PCIE_VENDOR_ID_ASIX, + .device = PCI_ANY_ID, + .subvendor = PCI_ANY_ID, + .subdevice = PCI_ANY_ID, + .init = pci_netmos_init, + .setup = pci_netmos_9900_setup, + }, /* * EndRun Technologies */ @@ -6065,6 +6078,10 @@ static const struct pci_device_id serial_pci_tbl[] = { 0xA000, 0x3002, 0, 0, pbn_NETMOS9900_2s_115200 }, + { PCIE_VENDOR_ID_ASIX, PCIE_DEVICE_ID_AX99100, + 0xA000, 0x1000, + 0, 0, pbn_b0_1_115200 }, + /* * Best Connectivity and Rosewill PCI Multi I/O cards */ From 59a33d83bbe6d73d2071d7ae21590b29faed0503 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:43 +0200 Subject: [PATCH 06/13] serial: 8250: Protect LCR write in shutdown MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The 8250_dw driver needs to potentially perform very complex operations during LCR writes because its BUSY handling prevents updates to LCR while UART is BUSY (which is not fully under our control without those complex operations). Thus, LCR writes should occur under port's lock. Move LCR write under port's lock in serial8250_do_shutdown(). Also split the LCR RMW so that the logic is on a separate line for clarity. Reported-by: Bandal, Shankar Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Cc: stable Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-2-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index a743964c9d22..20cf123a0540 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2348,6 +2348,7 @@ static int serial8250_startup(struct uart_port *port) void serial8250_do_shutdown(struct uart_port *port) { struct uart_8250_port *up = up_to_u8250p(port); + u32 lcr; serial8250_rpm_get(up); /* @@ -2374,13 +2375,13 @@ void serial8250_do_shutdown(struct uart_port *port) port->mctrl &= ~TIOCM_OUT2; serial8250_set_mctrl(port, port->mctrl); + + /* Disable break condition */ + lcr = serial_port_in(port, UART_LCR); + lcr &= ~UART_LCR_SBC; + serial_port_out(port, UART_LCR, lcr); } - /* - * Disable break condition and FIFOs - */ - serial_port_out(port, UART_LCR, - serial_port_in(port, UART_LCR) & ~UART_LCR_SBC); serial8250_clear_fifos(up); rsa_disable(up); From 8002d6d6d0d8a36a7d6ca523b17a51cb0fa7c3c3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:44 +0200 Subject: [PATCH 07/13] serial: 8250_dw: Avoid unnecessary LCR writes MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When DW UART is configured with BUSY flag, LCR writes may not always succeed which can make any LCR write complex and very expensive. Performing write directly can trigger IRQ and the driver has to perform complex and distruptive sequence while retrying the write. Therefore, it's better to avoid doing LCR write that would not change the value of the LCR register. Add LCR write avoidance code into the 8250_dw driver's .serial_out() functions. Reported-by: Bandal, Shankar Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Cc: stable Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-3-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dw.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index db73b2ae17fa..f47ede4d1968 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -181,6 +181,22 @@ static void dw8250_check_lcr(struct uart_port *p, unsigned int offset, u32 value */ } +/* + * With BUSY, LCR writes can be very expensive (IRQ + complex retry logic). + * If the write does not change the value of the LCR register, skip it entirely. + */ +static bool dw8250_can_skip_reg_write(struct uart_port *p, unsigned int offset, u32 value) +{ + struct dw8250_data *d = to_dw8250_data(p->private_data); + u32 lcr; + + if (offset != UART_LCR || d->uart_16550_compatible) + return false; + + lcr = serial_port_in(p, offset); + return lcr == value; +} + /* Returns once the transmitter is empty or we run out of retries */ static void dw8250_tx_wait_empty(struct uart_port *p) { @@ -207,12 +223,18 @@ static void dw8250_tx_wait_empty(struct uart_port *p) static void dw8250_serial_out(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + writeb(value, p->membase + (offset << p->regshift)); dw8250_check_lcr(p, offset, value); } static void dw8250_serial_out38x(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + /* Allow the TX to drain before we reconfigure */ if (offset == UART_LCR) dw8250_tx_wait_empty(p); @@ -237,6 +259,9 @@ static u32 dw8250_serial_inq(struct uart_port *p, unsigned int offset) static void dw8250_serial_outq(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + value &= 0xff; __raw_writeq(value, p->membase + (offset << p->regshift)); /* Read back to ensure register write ordering. */ @@ -248,6 +273,9 @@ static void dw8250_serial_outq(struct uart_port *p, unsigned int offset, u32 val static void dw8250_serial_out32(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + writel(value, p->membase + (offset << p->regshift)); dw8250_check_lcr(p, offset, value); } @@ -261,6 +289,9 @@ static u32 dw8250_serial_in32(struct uart_port *p, unsigned int offset) static void dw8250_serial_out32be(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + iowrite32be(value, p->membase + (offset << p->regshift)); dw8250_check_lcr(p, offset, value); } From 8324a54f604da18f21070702a8ad82ab2062787b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:45 +0200 Subject: [PATCH 08/13] serial: 8250: Add serial8250_handle_irq_locked() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 8250_port exports serial8250_handle_irq() to HW specific 8250 drivers. It takes port's lock within but a HW specific 8250 driver may want to take port's lock itself, do something, and then call the generic handler in 8250_port but to do that, the caller has to release port's lock for no good reason. Introduce serial8250_handle_irq_locked() which a HW specific driver can call while already holding port's lock. As this is new export, put it straight into a namespace (where all 8250 exports should eventually be moved). Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Cc: stable Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-4-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 24 ++++++++++++++++-------- include/linux/serial_8250.h | 1 + 2 files changed, 17 insertions(+), 8 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 20cf123a0540..14d6aca44551 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -18,6 +18,7 @@ #include #include #include +#include #include #include #include @@ -1782,20 +1783,16 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir) } /* - * This handles the interrupt from one port. + * Context: port's lock must be held by the caller. */ -int serial8250_handle_irq(struct uart_port *port, unsigned int iir) +void serial8250_handle_irq_locked(struct uart_port *port, unsigned int iir) { struct uart_8250_port *up = up_to_u8250p(port); struct tty_port *tport = &port->state->port; bool skip_rx = false; - unsigned long flags; u16 status; - if (iir & UART_IIR_NO_INT) - return 0; - - uart_port_lock_irqsave(port, &flags); + lockdep_assert_held_once(&port->lock); status = serial_lsr_in(up); @@ -1828,8 +1825,19 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) else if (!up->dma->tx_running) __stop_tx(up); } +} +EXPORT_SYMBOL_NS_GPL(serial8250_handle_irq_locked, "SERIAL_8250"); - uart_unlock_and_check_sysrq_irqrestore(port, flags); +/* + * This handles the interrupt from one port. + */ +int serial8250_handle_irq(struct uart_port *port, unsigned int iir) +{ + if (iir & UART_IIR_NO_INT) + return 0; + + guard(uart_port_lock_irqsave)(port); + serial8250_handle_irq_locked(port, iir); return 1; } diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 01efdce0fda0..a95b2d143d24 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -195,6 +195,7 @@ void serial8250_do_set_mctrl(struct uart_port *port, unsigned int mctrl); void serial8250_do_set_divisor(struct uart_port *port, unsigned int baud, unsigned int quot); int fsl8250_handle_irq(struct uart_port *port); +void serial8250_handle_irq_locked(struct uart_port *port, unsigned int iir); int serial8250_handle_irq(struct uart_port *port, unsigned int iir); u16 serial8250_rx_chars(struct uart_8250_port *up, u16 lsr); void serial8250_read_char(struct uart_8250_port *up, u16 lsr); From 883c5a2bc934c165c4491d1ef7da0ac4e9765077 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:46 +0200 Subject: [PATCH 09/13] serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit dw8250_handle_irq() takes port's lock multiple times with no good reason to release it in between and calls serial8250_handle_irq() that also takes port's lock. Take port's lock only once in dw8250_handle_irq() and use serial8250_handle_irq_locked() to avoid releasing port's lock in between. As IIR_NO_INT check in serial8250_handle_irq() was outside of port's lock, it has to be done already in dw8250_handle_irq(). DW UART can, in addition to IIR_NO_INT, report BUSY_DETECT (0x7) which collided with the IIR_NO_INT (0x1) check in serial8250_handle_irq() (because & is used instead of ==) meaning that no other work is done by serial8250_handle_irq() during an BUSY_DETECT interrupt. This allows reorganizing code in dw8250_handle_irq() to do both IIR_NO_INT and BUSY_DETECT handling right at the start simplifying the logic. Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Cc: stable Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-5-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dw.c | 37 ++++++++++++++++++------------- 1 file changed, 21 insertions(+), 16 deletions(-) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index f47ede4d1968..abf0814086a5 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -9,6 +9,9 @@ * LCR is written whilst busy. If it is, then a busy detect interrupt is * raised, the LCR needs to be rewritten and the uart status register read. */ +#include +#include +#include #include #include #include @@ -40,6 +43,8 @@ #define RZN1_UART_RDMACR 0x110 /* DMA Control Register Receive Mode */ /* DesignWare specific register fields */ +#define DW_UART_IIR_IID GENMASK(3, 0) + #define DW_UART_MCR_SIRE BIT(6) /* Renesas specific register fields */ @@ -312,7 +317,19 @@ static int dw8250_handle_irq(struct uart_port *p) bool rx_timeout = (iir & 0x3f) == UART_IIR_RX_TIMEOUT; unsigned int quirks = d->pdata->quirks; unsigned int status; - unsigned long flags; + + switch (FIELD_GET(DW_UART_IIR_IID, iir)) { + case UART_IIR_NO_INT: + return 0; + + case UART_IIR_BUSY: + /* Clear the USR */ + serial_port_in(p, d->pdata->usr_reg); + + return 1; + } + + guard(uart_port_lock_irqsave)(p); /* * There are ways to get Designware-based UARTs into a state where @@ -325,20 +342,15 @@ static int dw8250_handle_irq(struct uart_port *p) * so we limit the workaround only to non-DMA mode. */ if (!up->dma && rx_timeout) { - uart_port_lock_irqsave(p, &flags); status = serial_lsr_in(up); if (!(status & (UART_LSR_DR | UART_LSR_BI))) serial_port_in(p, UART_RX); - - uart_port_unlock_irqrestore(p, flags); } /* Manually stop the Rx DMA transfer when acting as flow controller */ if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) { - uart_port_lock_irqsave(p, &flags); status = serial_lsr_in(up); - uart_port_unlock_irqrestore(p, flags); if (status & (UART_LSR_DR | UART_LSR_BI)) { dw8250_writel_ext(p, RZN1_UART_RDMACR, 0); @@ -346,17 +358,9 @@ static int dw8250_handle_irq(struct uart_port *p) } } - if (serial8250_handle_irq(p, iir)) - return 1; + serial8250_handle_irq_locked(p, iir); - if ((iir & UART_IIR_BUSY) == UART_IIR_BUSY) { - /* Clear the USR */ - serial_port_in(p, d->pdata->usr_reg); - - return 1; - } - - return 0; + return 1; } static void dw8250_clk_work_cb(struct work_struct *work) @@ -867,6 +871,7 @@ static struct platform_driver dw8250_platform_driver = { module_platform_driver(dw8250_platform_driver); +MODULE_IMPORT_NS("SERIAL_8250"); MODULE_AUTHOR("Jamie Iles"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("Synopsys DesignWare 8250 serial port driver"); From 73a4ed8f9efaaaf8207614ccc1c9d5ca1888f23a Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:47 +0200 Subject: [PATCH 10/13] serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit INTC10EE UART can end up into an interrupt storm where it reports IIR_NO_INT (0x1). If the storm happens during active UART operation, it is promptly stopped by IIR value change due to Rx or Tx events. However, when there is no activity, either due to idle serial line or due to specific circumstances such as during shutdown that writes IER=0, there is nothing to stop the storm. During shutdown the storm is particularly problematic because serial8250_do_shutdown() calls synchronize_irq() that will hang in waiting for the storm to finish which never happens. This problem can also result in triggering a warning: irq 45: nobody cared (try booting with the "irqpoll" option) [...snip...] handlers: serial8250_interrupt Disabling IRQ #45 Normal means to reset interrupt status by reading LSR, MSR, USR, or RX register do not result in the UART deasserting the IRQ. Add a quirk to INTC10EE UARTs to enable Tx interrupts if UART's Tx is currently empty and inactive. Rework IIR_NO_INT to keep track of the number of consecutive IIR_NO_INT, and on fourth one perform the quirk. Enabling Tx interrupts should change IIR value from IIR_NO_INT to IIR_THRI which has been observed to stop the storm. Fixes: e92fad024929 ("serial: 8250_dw: Add ACPI ID for Granite Rapids-D UART") Cc: stable Reported-by: Bandal, Shankar Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-6-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dw.c | 67 +++++++++++++++++++++++++++++-- 1 file changed, 63 insertions(+), 4 deletions(-) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index abf0814086a5..3d8032f752b8 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -61,6 +61,13 @@ #define DW_UART_QUIRK_IS_DMA_FC BIT(3) #define DW_UART_QUIRK_APMC0D08 BIT(4) #define DW_UART_QUIRK_CPR_VALUE BIT(5) +#define DW_UART_QUIRK_IER_KICK BIT(6) + +/* + * Number of consecutive IIR_NO_INT interrupts required to trigger interrupt + * storm prevention code. + */ +#define DW_UART_QUIRK_IER_KICK_THRES 4 struct dw8250_platform_data { u8 usr_reg; @@ -82,6 +89,8 @@ struct dw8250_data { unsigned int skip_autocfg:1; unsigned int uart_16550_compatible:1; + + u8 no_int_count; }; static inline struct dw8250_data *to_dw8250_data(struct dw8250_port_data *data) @@ -308,6 +317,29 @@ static u32 dw8250_serial_in32be(struct uart_port *p, unsigned int offset) return dw8250_modify_msr(p, offset, value); } +/* + * INTC10EE UART can IRQ storm while reporting IIR_NO_INT. Inducing IIR value + * change has been observed to break the storm. + * + * If Tx is empty (THRE asserted), we use here IER_THRI to cause IIR_NO_INT -> + * IIR_THRI transition. + */ +static void dw8250_quirk_ier_kick(struct uart_port *p) +{ + struct uart_8250_port *up = up_to_u8250p(p); + u32 lsr; + + if (up->ier & UART_IER_THRI) + return; + + lsr = serial_lsr_in(up); + if (!(lsr & UART_LSR_THRE)) + return; + + serial_port_out(p, UART_IER, up->ier | UART_IER_THRI); + serial_port_in(p, UART_LCR); /* safe, no side-effects */ + serial_port_out(p, UART_IER, up->ier); +} static int dw8250_handle_irq(struct uart_port *p) { @@ -318,18 +350,30 @@ static int dw8250_handle_irq(struct uart_port *p) unsigned int quirks = d->pdata->quirks; unsigned int status; + guard(uart_port_lock_irqsave)(p); + switch (FIELD_GET(DW_UART_IIR_IID, iir)) { case UART_IIR_NO_INT: + if (d->uart_16550_compatible || up->dma) + return 0; + + if (quirks & DW_UART_QUIRK_IER_KICK && + d->no_int_count == (DW_UART_QUIRK_IER_KICK_THRES - 1)) + dw8250_quirk_ier_kick(p); + d->no_int_count = (d->no_int_count + 1) % DW_UART_QUIRK_IER_KICK_THRES; + return 0; case UART_IIR_BUSY: /* Clear the USR */ serial_port_in(p, d->pdata->usr_reg); + d->no_int_count = 0; + return 1; } - guard(uart_port_lock_irqsave)(p); + d->no_int_count = 0; /* * There are ways to get Designware-based UARTs into a state where @@ -562,6 +606,14 @@ static void dw8250_reset_control_assert(void *data) reset_control_assert(data); } +static void dw8250_shutdown(struct uart_port *port) +{ + struct dw8250_data *d = to_dw8250_data(port->private_data); + + serial8250_do_shutdown(port); + d->no_int_count = 0; +} + static int dw8250_probe(struct platform_device *pdev) { struct uart_8250_port uart = {}, *up = &uart; @@ -689,10 +741,12 @@ static int dw8250_probe(struct platform_device *pdev) dw8250_quirks(p, data); /* If the Busy Functionality is not implemented, don't handle it */ - if (data->uart_16550_compatible) + if (data->uart_16550_compatible) { p->handle_irq = NULL; - else if (data->pdata) + } else if (data->pdata) { p->handle_irq = dw8250_handle_irq; + p->shutdown = dw8250_shutdown; + } dw8250_setup_dma_filter(p, data); @@ -824,6 +878,11 @@ static const struct dw8250_platform_data dw8250_skip_set_rate_data = { .quirks = DW_UART_QUIRK_SKIP_SET_RATE, }; +static const struct dw8250_platform_data dw8250_intc10ee = { + .usr_reg = DW_UART_USR, + .quirks = DW_UART_QUIRK_IER_KICK, +}; + static const struct of_device_id dw8250_of_match[] = { { .compatible = "snps,dw-apb-uart", .data = &dw8250_dw_apb }, { .compatible = "cavium,octeon-3860-uart", .data = &dw8250_octeon_3860_data }, @@ -853,7 +912,7 @@ static const struct acpi_device_id dw8250_acpi_match[] = { { "INT33C5", (kernel_ulong_t)&dw8250_dw_apb }, { "INT3434", (kernel_ulong_t)&dw8250_dw_apb }, { "INT3435", (kernel_ulong_t)&dw8250_dw_apb }, - { "INTC10EE", (kernel_ulong_t)&dw8250_dw_apb }, + { "INTC10EE", (kernel_ulong_t)&dw8250_intc10ee }, { }, }; MODULE_DEVICE_TABLE(acpi, dw8250_acpi_match); From e0a368ae79531ff92105a2692f10d83052055856 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:48 +0200 Subject: [PATCH 11/13] serial: 8250: Add late synchronize_irq() to shutdown to handle DW UART BUSY MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When DW UART is !uart_16550_compatible, it can indicate BUSY at any point (when under constant Rx pressure) unless a complex sequence of steps is performed. Any LCR write can run a foul with the condition that prevents writing LCR while the UART is BUSY, which triggers BUSY_DETECT interrupt that seems unmaskable using IER bits. Normal flow is that dw8250_handle_irq() handles BUSY_DETECT condition by reading USR register. This BUSY feature, however, breaks the assumptions made in serial8250_do_shutdown(), which runs synchronize_irq() after clearing IER and assumes no interrupts can occur after that point but then proceeds to update LCR, which on DW UART can trigger an interrupt. If serial8250_do_shutdown() releases the interrupt handler before the handler has run and processed the BUSY_DETECT condition by read the USR register, the IRQ is not deasserted resulting in interrupt storm that triggers "irq x: nobody cared" warning leading to disabling the IRQ. Add late synchronize_irq() into serial8250_do_shutdown() to ensure BUSY_DETECT from DW UART is handled before port's interrupt handler is released. Alternative would be to add DW UART specific shutdown function but it would mostly duplicate the generic code and the extra synchronize_irq() seems pretty harmless in serial8250_do_shutdown(). Fixes: 7d4008ebb1c9 ("tty: add a DesignWare 8250 driver") Cc: stable Reported-by: Bandal, Shankar Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-7-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 14d6aca44551..94a64b3dd1f7 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2399,6 +2399,12 @@ void serial8250_do_shutdown(struct uart_port *port) * the IRQ chain. */ serial_port_in(port, UART_RX); + /* + * LCR writes on DW UART can trigger late (unmaskable) IRQs. + * Handle them before releasing the handler. + */ + synchronize_irq(port->irq); + serial8250_rpm_put(up); up->ops->release_irq(up); From a7b9ce39fbe4ae2919fe4f7ac16c293cb6632d30 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Tue, 3 Feb 2026 19:10:49 +0200 Subject: [PATCH 12/13] serial: 8250_dw: Ensure BUSY is deasserted MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit DW UART cannot write to LCR, DLL, and DLH while BUSY is asserted. Existance of BUSY depends on uart_16550_compatible, if UART HW is configured with it those registers can always be written. There currently is dw8250_force_idle() which attempts to achieve non-BUSY state by disabling FIFO, however, the solution is unreliable when Rx keeps getting more and more characters. Create a sequence of operations that ensures UART cannot keep BUSY asserted indefinitely. The new sequence relies on enabling loopback mode temporarily to prevent incoming Rx characters keeping UART BUSY. Ensure no Tx in ongoing while the UART is switches into the loopback mode (requires exporting serial8250_fifo_wait_for_lsr_thre() and adding DMA Tx pause/resume functions). According to tests performed by Adriana Nicolae , simply disabling FIFO or clearing FIFOs only once does not always ensure BUSY is deasserted but up to two tries may be needed. This could be related to ongoing Rx of a character (a guess, not known for sure). Therefore, retry FIFO clearing a few times (retry limit 4 is arbitrary number but using, e.g., p->fifosize seems overly large). Tests performed by others did not exhibit similar challenge but it does not seem harmful to leave the FIFO clearing loop in place for all DW UARTs with BUSY functionality. Use the new dw8250_idle_enter/exit() to do divisor writes and LCR writes. In case of plain LCR writes, opportunistically try to update LCR first and only invoke dw8250_idle_enter() if the write did not succeed (it has been observed that in practice most LCR writes do succeed without complications). This issue was first reported by qianfan Zhao who put lots of debugging effort into understanding the solution space. Fixes: c49436b657d0 ("serial: 8250_dw: Improve unwritable LCR workaround") Fixes: 7d4008ebb1c9 ("tty: add a DesignWare 8250 driver") Cc: stable Reported-by: qianfan Zhao Link: https://lore.kernel.org/linux-serial/289bb78a-7509-1c5c-2923-a04ed3b6487d@163.com/ Reported-by: Adriana Nicolae Link: https://lore.kernel.org/linux-serial/20250819182322.3451959-1-adriana@arista.com/ Reported-by: Bandal, Shankar Tested-by: Bandal, Shankar Tested-by: Murthy, Shanth Reviewed-by: Andy Shevchenko Signed-off-by: Ilpo Järvinen Link: https://patch.msgid.link/20260203171049.4353-8-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250.h | 25 ++++ drivers/tty/serial/8250/8250_dw.c | 171 ++++++++++++++++++++-------- drivers/tty/serial/8250/8250_port.c | 28 ++--- 3 files changed, 165 insertions(+), 59 deletions(-) diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h index 8caecfc85d93..77fe0588fd6b 100644 --- a/drivers/tty/serial/8250/8250.h +++ b/drivers/tty/serial/8250/8250.h @@ -175,7 +175,9 @@ static unsigned int __maybe_unused serial_icr_read(struct uart_8250_port *up, return value; } +void serial8250_clear_fifos(struct uart_8250_port *p); void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p); +void serial8250_fifo_wait_for_lsr_thre(struct uart_8250_port *up, unsigned int count); void serial8250_rpm_get(struct uart_8250_port *p); void serial8250_rpm_put(struct uart_8250_port *p); @@ -400,6 +402,26 @@ static inline bool serial8250_tx_dma_running(struct uart_8250_port *p) return dma && dma->tx_running; } + +static inline void serial8250_tx_dma_pause(struct uart_8250_port *p) +{ + struct uart_8250_dma *dma = p->dma; + + if (!dma->tx_running) + return; + + dmaengine_pause(dma->txchan); +} + +static inline void serial8250_tx_dma_resume(struct uart_8250_port *p) +{ + struct uart_8250_dma *dma = p->dma; + + if (!dma->tx_running) + return; + + dmaengine_resume(dma->txchan); +} #else static inline int serial8250_tx_dma(struct uart_8250_port *p) { @@ -421,6 +443,9 @@ static inline bool serial8250_tx_dma_running(struct uart_8250_port *p) { return false; } + +static inline void serial8250_tx_dma_pause(struct uart_8250_port *p) { } +static inline void serial8250_tx_dma_resume(struct uart_8250_port *p) { } #endif static inline int ns16550a_goto_highspeed(struct uart_8250_port *up) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index 3d8032f752b8..94beadb4024d 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -47,6 +48,8 @@ #define DW_UART_MCR_SIRE BIT(6) +#define DW_UART_USR_BUSY BIT(0) + /* Renesas specific register fields */ #define RZN1_UART_xDMACR_DMA_EN BIT(0) #define RZN1_UART_xDMACR_1_WORD_BURST (0 << 1) @@ -89,6 +92,7 @@ struct dw8250_data { unsigned int skip_autocfg:1; unsigned int uart_16550_compatible:1; + unsigned int in_idle:1; u8 no_int_count; }; @@ -121,78 +125,151 @@ static inline u32 dw8250_modify_msr(struct uart_port *p, unsigned int offset, u3 return value; } -/* - * This function is being called as part of the uart_port::serial_out() - * routine. Hence, it must not call serial_port_out() or serial_out() - * against the modified registers here, i.e. LCR. - */ -static void dw8250_force_idle(struct uart_port *p) +static void dw8250_idle_exit(struct uart_port *p) { + struct dw8250_data *d = to_dw8250_data(p->private_data); struct uart_8250_port *up = up_to_u8250p(p); - unsigned int lsr; - /* - * The following call currently performs serial_out() - * against the FCR register. Because it differs to LCR - * there will be no infinite loop, but if it ever gets - * modified, we might need a new custom version of it - * that avoids infinite recursion. - */ - serial8250_clear_and_reinit_fifos(up); + if (d->uart_16550_compatible) + return; - /* - * With PSLVERR_RESP_EN parameter set to 1, the device generates an - * error response when an attempt to read an empty RBR with FIFO - * enabled. - */ - if (up->fcr & UART_FCR_ENABLE_FIFO) { - lsr = serial_port_in(p, UART_LSR); - if (!(lsr & UART_LSR_DR)) - return; + if (up->capabilities & UART_CAP_FIFO) + serial_port_out(p, UART_FCR, up->fcr); + serial_port_out(p, UART_MCR, up->mcr); + serial_port_out(p, UART_IER, up->ier); + + /* DMA Rx is restarted by IRQ handler as needed. */ + if (up->dma) + serial8250_tx_dma_resume(up); + + d->in_idle = 0; +} + +/* + * Ensure BUSY is not asserted. If DW UART is configured with + * !uart_16550_compatible, the writes to LCR, DLL, and DLH fail while + * BUSY is asserted. + * + * Context: port's lock must be held + */ +static int dw8250_idle_enter(struct uart_port *p) +{ + struct dw8250_data *d = to_dw8250_data(p->private_data); + unsigned int usr_reg = d->pdata ? d->pdata->usr_reg : DW_UART_USR; + struct uart_8250_port *up = up_to_u8250p(p); + int retries; + u32 lsr; + + lockdep_assert_held_once(&p->lock); + + if (d->uart_16550_compatible) + return 0; + + d->in_idle = 1; + + /* Prevent triggering interrupt from RBR filling */ + serial_port_out(p, UART_IER, 0); + + if (up->dma) { + serial8250_rx_dma_flush(up); + if (serial8250_tx_dma_running(up)) + serial8250_tx_dma_pause(up); } - serial_port_in(p, UART_RX); + /* + * Wait until Tx becomes empty + one extra frame time to ensure all bits + * have been sent on the wire. + * + * FIXME: frame_time delay is too long with very low baudrates. + */ + serial8250_fifo_wait_for_lsr_thre(up, p->fifosize); + ndelay(p->frame_time); + + serial_port_out(p, UART_MCR, up->mcr | UART_MCR_LOOP); + + retries = 4; /* Arbitrary limit, 2 was always enough in tests */ + do { + serial8250_clear_fifos(up); + if (!(serial_port_in(p, usr_reg) & DW_UART_USR_BUSY)) + break; + /* FIXME: frame_time delay is too long with very low baudrates. */ + ndelay(p->frame_time); + } while (--retries); + + lsr = serial_lsr_in(up); + if (lsr & UART_LSR_DR) { + serial_port_in(p, UART_RX); + up->lsr_saved_flags = 0; + } + + /* Now guaranteed to have BUSY deasserted? Just sanity check */ + if (serial_port_in(p, usr_reg) & DW_UART_USR_BUSY) { + dw8250_idle_exit(p); + return -EBUSY; + } + + return 0; +} + +static void dw8250_set_divisor(struct uart_port *p, unsigned int baud, + unsigned int quot, unsigned int quot_frac) +{ + struct uart_8250_port *up = up_to_u8250p(p); + int ret; + + ret = dw8250_idle_enter(p); + if (ret < 0) + return; + + serial_port_out(p, UART_LCR, up->lcr | UART_LCR_DLAB); + if (!(serial_port_in(p, UART_LCR) & UART_LCR_DLAB)) + goto idle_failed; + + serial_dl_write(up, quot); + serial_port_out(p, UART_LCR, up->lcr); + +idle_failed: + dw8250_idle_exit(p); } /* * This function is being called as part of the uart_port::serial_out() - * routine. Hence, it must not call serial_port_out() or serial_out() - * against the modified registers here, i.e. LCR. + * routine. Hence, special care must be taken when serial_port_out() or + * serial_out() against the modified registers here, i.e. LCR (d->in_idle is + * used to break recursion loop). */ static void dw8250_check_lcr(struct uart_port *p, unsigned int offset, u32 value) { struct dw8250_data *d = to_dw8250_data(p->private_data); - void __iomem *addr = p->membase + (offset << p->regshift); - int tries = 1000; + u32 lcr; + int ret; if (offset != UART_LCR || d->uart_16550_compatible) return; + lcr = serial_port_in(p, UART_LCR); + /* Make sure LCR write wasn't ignored */ - while (tries--) { - u32 lcr = serial_port_in(p, offset); + if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR)) + return; - if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR)) - return; + if (d->in_idle) + goto write_err; - dw8250_force_idle(p); + ret = dw8250_idle_enter(p); + if (ret < 0) + goto write_err; -#ifdef CONFIG_64BIT - if (p->type == PORT_OCTEON) - __raw_writeq(value & 0xff, addr); - else -#endif - if (p->iotype == UPIO_MEM32) - writel(value, addr); - else if (p->iotype == UPIO_MEM32BE) - iowrite32be(value, addr); - else - writeb(value, addr); - } + serial_port_out(p, UART_LCR, value); + dw8250_idle_exit(p); + return; + +write_err: /* * FIXME: this deadlocks if port->lock is already held * dev_err(p->dev, "Couldn't set LCR to %d\n", value); */ + return; /* Silences "label at the end of compound statement" */ } /* @@ -632,8 +709,10 @@ static int dw8250_probe(struct platform_device *pdev) p->type = PORT_8250; p->flags = UPF_FIXED_PORT; p->dev = dev; + p->set_ldisc = dw8250_set_ldisc; p->set_termios = dw8250_set_termios; + p->set_divisor = dw8250_set_divisor; data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL); if (!data) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 94a64b3dd1f7..328711b5df1a 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -489,7 +489,7 @@ serial_port_out_sync(struct uart_port *p, int offset, int value) /* * FIFO support. */ -static void serial8250_clear_fifos(struct uart_8250_port *p) +void serial8250_clear_fifos(struct uart_8250_port *p) { if (p->capabilities & UART_CAP_FIFO) { serial_out(p, UART_FCR, UART_FCR_ENABLE_FIFO); @@ -498,6 +498,7 @@ static void serial8250_clear_fifos(struct uart_8250_port *p) serial_out(p, UART_FCR, 0); } } +EXPORT_SYMBOL_NS_GPL(serial8250_clear_fifos, "SERIAL_8250"); static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t); static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t); @@ -3198,6 +3199,17 @@ void serial8250_set_defaults(struct uart_8250_port *up) } EXPORT_SYMBOL_GPL(serial8250_set_defaults); +void serial8250_fifo_wait_for_lsr_thre(struct uart_8250_port *up, unsigned int count) +{ + unsigned int i; + + for (i = 0; i < count; i++) { + if (wait_for_lsr(up, UART_LSR_THRE)) + return; + } +} +EXPORT_SYMBOL_NS_GPL(serial8250_fifo_wait_for_lsr_thre, "SERIAL_8250"); + #ifdef CONFIG_SERIAL_8250_CONSOLE static void serial8250_console_putchar(struct uart_port *port, unsigned char ch) @@ -3239,16 +3251,6 @@ static void serial8250_console_restore(struct uart_8250_port *up) serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS); } -static void fifo_wait_for_lsr(struct uart_8250_port *up, unsigned int count) -{ - unsigned int i; - - for (i = 0; i < count; i++) { - if (wait_for_lsr(up, UART_LSR_THRE)) - return; - } -} - /* * Print a string to the serial port using the device FIFO * @@ -3267,7 +3269,7 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up, while (s != end) { /* Allow timeout for each byte of a possibly full FIFO */ - fifo_wait_for_lsr(up, fifosize); + serial8250_fifo_wait_for_lsr_thre(up, fifosize); for (i = 0; i < fifosize && s != end; ++i) { if (*s == '\n' && !cr_sent) { @@ -3285,7 +3287,7 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up, * Allow timeout for each byte written since the caller will only wait * for UART_LSR_BOTH_EMPTY using the timeout of a single character */ - fifo_wait_for_lsr(up, tx_count); + serial8250_fifo_wait_for_lsr_thre(up, tx_count); } /* From 5eb608319bb56464674a71b4a66ea65c6c435d64 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Tue, 27 Jan 2026 17:56:01 -0500 Subject: [PATCH 13/13] vt: save/restore unicode screen buffer for alternate screen The alternate screen support added by commit 23743ba64709 ("vt: add support for smput/rmput escape codes") only saves and restores the regular screen buffer (vc_origin), but completely ignores the corresponding unicode screen buffer (vc_uni_lines) creating a messed-up display. Add vc_saved_uni_lines to save the unicode screen buffer when entering the alternate screen, and restore it when leaving. Also ensure proper cleanup in reset_terminal() and vc_deallocate(). Fixes: 23743ba64709 ("vt: add support for smput/rmput escape codes") Cc: stable Signed-off-by: Nicolas Pitre Link: https://patch.msgid.link/5o2p6qp3-91pq-0p17-or02-1oors4417ns7@onlyvoer.pbz Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/vt.c | 8 ++++++++ include/linux/console_struct.h | 1 + 2 files changed, 9 insertions(+) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index c1f152d8b03b..e2df99e3d458 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -1339,6 +1339,8 @@ struct vc_data *vc_deallocate(unsigned int currcons) kfree(vc->vc_saved_screen); vc->vc_saved_screen = NULL; } + vc_uniscr_free(vc->vc_saved_uni_lines); + vc->vc_saved_uni_lines = NULL; } return vc; } @@ -1884,6 +1886,8 @@ static void enter_alt_screen(struct vc_data *vc) vc->vc_saved_screen = kmemdup((u16 *)vc->vc_origin, size, GFP_KERNEL); if (vc->vc_saved_screen == NULL) return; + vc->vc_saved_uni_lines = vc->vc_uni_lines; + vc->vc_uni_lines = NULL; vc->vc_saved_rows = vc->vc_rows; vc->vc_saved_cols = vc->vc_cols; save_cur(vc); @@ -1905,6 +1909,8 @@ static void leave_alt_screen(struct vc_data *vc) dest = ((u16 *)vc->vc_origin) + r * vc->vc_cols; memcpy(dest, src, 2 * cols); } + vc_uniscr_set(vc, vc->vc_saved_uni_lines); + vc->vc_saved_uni_lines = NULL; restore_cur(vc); /* Update the entire screen */ if (con_should_update(vc)) @@ -2227,6 +2233,8 @@ static void reset_terminal(struct vc_data *vc, int do_clear) if (vc->vc_saved_screen != NULL) { kfree(vc->vc_saved_screen); vc->vc_saved_screen = NULL; + vc_uniscr_free(vc->vc_saved_uni_lines); + vc->vc_saved_uni_lines = NULL; vc->vc_saved_rows = 0; vc->vc_saved_cols = 0; } diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h index 13b35637bd5a..d5ca855116df 100644 --- a/include/linux/console_struct.h +++ b/include/linux/console_struct.h @@ -160,6 +160,7 @@ struct vc_data { struct uni_pagedict **uni_pagedict_loc; /* [!] Location of uni_pagedict variable for this console */ u32 **vc_uni_lines; /* unicode screen content */ u16 *vc_saved_screen; + u32 **vc_saved_uni_lines; unsigned int vc_saved_cols; unsigned int vc_saved_rows; /* additional information is in vt_kern.h */