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The following splat has been observed on a SAMA5D27 platform using atmel_serial: BUG: sleeping function called from invalid context at kernel/irq/manage.c:738 in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 27, name: kworker/u5:0 preempt_count: 1, expected: 0 INFO: lockdep is turned off. irq event stamp: 0 hardirqs last enabled at (0): [<00000000>] 0x0 hardirqs last disabled at (0): [<c01588f0>] copy_process+0x1c4c/0x7bec softirqs last enabled at (0): [<c0158944>] copy_process+0x1ca0/0x7bec softirqs last disabled at (0): [<00000000>] 0x0 CPU: 0 UID: 0 PID: 27 Comm: kworker/u5:0 Not tainted 6.13.0-rc7+ #74 Hardware name: Atmel SAMA5 Workqueue: hci0 hci_power_on [bluetooth] Call trace: unwind_backtrace from show_stack+0x18/0x1c show_stack from dump_stack_lvl+0x44/0x70 dump_stack_lvl from __might_resched+0x38c/0x598 __might_resched from disable_irq+0x1c/0x48 disable_irq from mctrl_gpio_disable_ms+0x74/0xc0 mctrl_gpio_disable_ms from atmel_disable_ms.part.0+0x80/0x1f4 atmel_disable_ms.part.0 from atmel_set_termios+0x764/0x11e8 atmel_set_termios from uart_change_line_settings+0x15c/0x994 uart_change_line_settings from uart_set_termios+0x2b0/0x668 uart_set_termios from tty_set_termios+0x600/0x8ec tty_set_termios from ttyport_set_flow_control+0x188/0x1e0 ttyport_set_flow_control from wilc_setup+0xd0/0x524 [hci_wilc] wilc_setup [hci_wilc] from hci_dev_open_sync+0x330/0x203c [bluetooth] hci_dev_open_sync [bluetooth] from hci_dev_do_open+0x40/0xb0 [bluetooth] hci_dev_do_open [bluetooth] from hci_power_on+0x12c/0x664 [bluetooth] hci_power_on [bluetooth] from process_one_work+0x998/0x1a38 process_one_work from worker_thread+0x6e0/0xfb4 worker_thread from kthread+0x3d4/0x484 kthread from ret_from_fork+0x14/0x28 This warning is emitted when trying to toggle, at the highest level, some flow control (with serdev_device_set_flow_control) in a device driver. At the lowest level, the atmel_serial driver is using serial_mctrl_gpio lib to enable/disable the corresponding IRQs accordingly. The warning emitted by CONFIG_DEBUG_ATOMIC_SLEEP is due to disable_irq (called in mctrl_gpio_disable_ms) being possibly called in some atomic context (some tty drivers perform modem lines configuration in regions protected by port lock). Split mctrl_gpio_disable_ms into two differents APIs, a non-blocking one and a blocking one. Replace mctrl_gpio_disable_ms calls with the relevant version depending on whether the call is protected by some port lock. Suggested-by: Jiri Slaby <jirislaby@kernel.org> Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com> Acked-by: Richard Genoud <richard.genoud@bootlin.com> Link: https://lore.kernel.org/r/20250217-atomic_sleep_mctrl_serial_gpio-v3-1-59324b313eef@bootlin.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
107 lines
3.4 KiB
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107 lines
3.4 KiB
ReStructuredText
====================
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Low Level Serial API
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====================
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This document is meant as a brief overview of some aspects of the new serial
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driver. It is not complete, any questions you have should be directed to
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<rmk@arm.linux.org.uk>
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The reference implementation is contained within amba-pl011.c.
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Low Level Serial Hardware Driver
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--------------------------------
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The low level serial hardware driver is responsible for supplying port
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information (defined by uart_port) and a set of control methods (defined
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by uart_ops) to the core serial driver. The low level driver is also
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responsible for handling interrupts for the port, and providing any
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console support.
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Console Support
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---------------
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The serial core provides a few helper functions. This includes identifying
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the correct port structure (via uart_get_console()) and decoding command line
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arguments (uart_parse_options()).
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There is also a helper function (uart_console_write()) which performs a
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character by character write, translating newlines to CRLF sequences.
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Driver writers are recommended to use this function rather than implementing
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their own version.
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Locking
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-------
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It is the responsibility of the low level hardware driver to perform the
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necessary locking using port->lock. There are some exceptions (which
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are described in the struct uart_ops listing below.)
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There are two locks. A per-port spinlock, and an overall semaphore.
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From the core driver perspective, the port->lock locks the following
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data::
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port->mctrl
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port->icount
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port->state->xmit.head (circ_buf->head)
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port->state->xmit.tail (circ_buf->tail)
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The low level driver is free to use this lock to provide any additional
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locking.
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The port_sem semaphore is used to protect against ports being added/
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removed or reconfigured at inappropriate times. Since v2.6.27, this
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semaphore has been the 'mutex' member of the tty_port struct, and
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commonly referred to as the port mutex.
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uart_ops
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--------
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.. kernel-doc:: include/linux/serial_core.h
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:identifiers: uart_ops
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Other functions
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---------------
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.. kernel-doc:: drivers/tty/serial/serial_core.c
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:identifiers: uart_update_timeout uart_get_baud_rate uart_get_divisor
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uart_match_port uart_write_wakeup uart_register_driver
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uart_unregister_driver uart_suspend_port uart_resume_port
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uart_add_one_port uart_remove_one_port uart_console_write
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uart_parse_earlycon uart_parse_options uart_set_options
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uart_get_lsr_info uart_handle_dcd_change uart_handle_cts_change
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uart_try_toggle_sysrq uart_get_console
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.. kernel-doc:: include/linux/serial_core.h
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:identifiers: uart_port_tx_limited uart_port_tx
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Other notes
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-----------
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It is intended some day to drop the 'unused' entries from uart_port, and
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allow low level drivers to register their own individual uart_port's with
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the core. This will allow drivers to use uart_port as a pointer to a
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structure containing both the uart_port entry with their own extensions,
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thus::
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struct my_port {
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struct uart_port port;
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int my_stuff;
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};
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Modem control lines via GPIO
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----------------------------
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Some helpers are provided in order to set/get modem control lines via GPIO.
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.. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c
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:identifiers: mctrl_gpio_init mctrl_gpio_to_gpiod
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mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms
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mctrl_gpio_disable_ms_sync mctrl_gpio_disable_ms_no_sync
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