On Tue, Mar 12, 2019 at 03:55:54PM +0100, Hans de Goede wrote: > 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@xxxxxxxxxx> Applied to for-current, thanks!
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