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Before this commit the i2c-designware-platdrv assumes that if the pdev has an apci-companion it should use a dynamic adapter-nr and it sets adapter->nr to -1, otherwise it will use pdev->id as adapter->nr. There are 3 ways how platform_device-s to which i2c-designware-platdrv will bind can be instantiated: 1) Through of / devicetree 2) Through ACPI enumeration 3) Explicitly instantiated through platform_device_create + add 1) In case of devicetree-instantiation the drivers/of code always sets pdev->id to PLATFORM_DEVID_NONE, which is -1 so in this case both paths to set adapter->nr end up doing the same thing. 2) In case of ACPI instantiation the device will always have an ACPI-companion, so we are already using dynamic adapter-nrs. 3) There are 2 places manually instantiating a designware_i2c platform_dev: drivers/mfd/intel_quark_i2c_gpio.c drivers/mfd/intel-lpss.c In the intel_quark_i2c_gpio.c case pdev->id is always 0, so switching to dynamic adapter-nrs here could lead to the bus-number no longer being stable, but the quark X1000 only has 1 i2c-controller, which will also be assigned bus-number 0 when using dynamic adapter-nrs. In the intel-lpss.c case intel_lpss_probe() is called from either intel-lpss-acpi.c in which case there always is an ACPI-companion, or from intel-lpss-pci.c. In most cases devices handled by intel-lpss-pci.c also have an ACPI-companion, so we use a dynamic adapter-nr. But in some cases the ACPI-companion is missing and we would use pdev->id (allocated from intel_lpss_devid_ida). Devices which use the intel-lpss-pci.c code typically have many i2c busses, so using pdev->id in this case may lead to a bus-number conflict, triggering a WARN(id < 0, "couldn't get idr") in i2c-core-base.c causing an oops an the adapter registration to fail. So in this case using non dynamic adapter-nrs is actually undesirable. One machine on which this oops was triggering is the Apollo Lake based Acer TravelMate Spin B118. TL;DR: Switching to always using dynamic adapter-numbers does not make any difference in most cases and in the one case where it does make a difference the behavior change is desirable because the old behavior caused an oops. BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1687065 Signed-off-by: Hans de Goede <hdegoede@redhat.com> Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.