[Bug 96571] New: [CHV] Backlight init fails on Surface 3 if module load order is wrong

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96571

            Bug ID: 96571
           Summary: [CHV] Backlight init fails on Surface 3 if module load
                    order is wrong
           Product: DRI
           Version: XOrg git
          Hardware: All
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: stephenjust at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

As stated by Jani in https://bugs.freedesktop.org/show_bug.cgi?id=85977#c38, if
i915 is loaded before relevant PMIC/I2C/PWM drivers, PWM backlight probe can
fail.

[drm:pwm_setup_backlight [i915]] *ERROR* Failed to own the pwm chip

It would be nice to have this fixed so that the backlight on Surface 3 might
work reliably on distro-stock kernels that don't build-in certain modules to
influence the probe order.

Quote from Bug 85977:
>There still remains the issue with probe ordering: if i915 gets probed before all >the related pmic/i2c drivers, pwm_get() fails as described in comment #32. If you >want to file a new bug for that, I don't mind.
>
>As a workaround, these config options worked for me on Surface 3 PMIC backlight:
>
>CONFIG_PWM=y
>CONFIG_PWM_CRC=y
>CONFIG_I2C_DESIGNWARE_PLATFORM=y
>CONFIG_I2C_DESIGNWARE_PCI=y
>CONFIG_INTEL_SOC_PMIC=y
>CONFIG_DRM_I915=m

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