Subject: [Bug 199471] windfarm_pm72 no longer gets automatically loaded when CONFIG_I2C_POWERMAC=y is set (regression)

From: [email-masked]
Date: Sun, 01 Mar 2020 19:17:30 +0000

https://bugzilla.kernel.org/show_bug.cgi?id=199471

--- Comment #10 from Erhard F. ([email-masked]) ---
Created attachment 287743
  --> https://bugzilla.kernel.org/attachment.cgi?id=287743&action=edit
bisect.log

Finally checked on that bug again and bisected it. The offending commit is:

# git bisect bad | tee -a ~/bisect02.log 
af503716ac1444db61d80cb6d17cfe62929c21df is the first bad commit
commit af503716ac1444db61d80cb6d17cfe62929c21df
Author: Javier Martinez Canillas <[email-masked]>
Date:   Sun Dec 3 22:40:50 2017 +0100

    i2c: core: report OF style module alias for devices registered via OF

    The buses should honor the firmware interface used to register the device,
    but the I2C core reports a MODALIAS of the form i2c:<device> even for I2C
    devices registered via OF.

    This means that user-space will never get an OF stype uevent MODALIAS even
    when the drivers modules contain aliases exported from both the I2C and OF
    device ID tables. For example, an Atmel maXTouch Touchscreen registered by
    a DT node with compatible "atmel,maxtouch" has the following module alias:

    $ cat /sys/class/i2c-adapter/i2c-8/8-004b/modalias
    i2c:maxtouch

    So udev won't be able to auto-load a module for an OF-only device driver.
    Many OF-only drivers duplicate the OF device ID table entries in an I2C ID
    table only has a workaround for how the I2C core reports the module alias.

    This patch changes the I2C core to report an OF related MODALIAS uevent if
    the device was registered via OF. So for the previous example, after this
    patch, the reported MODALIAS for the Atmel maXTouch will be the following:

    $ cat /sys/class/i2c-adapter/i2c-8/8-004b/modalias
    of:NtrackpadT<NULL>Catmel,maxtouch

    NOTE: This patch may break out-of-tree drivers that were relying on this
          behavior, and only had an I2C device ID table even when the device
          was registered via OF. There are no remaining drivers in mainline
          that do this, but out-of-tree drivers have to be fixed and define
          a proper OF device ID table to have module auto-loading working.

    Signed-off-by: Javier Martinez Canillas <[email-masked]>
    Tested-by: Dmitry Mastykin <[email-masked]>
    Signed-off-by: Wolfram Sang <[email-masked]>

 drivers/i2c/i2c-core-base.c | 8 ++++++++
 1 file changed, 8 insertions(+)

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