[Bug 111095] New: Backlight flicker after suspend on certain Intel CherryTrail tablets

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111095

            Bug ID: 111095
           Summary: Backlight flicker after suspend on certain Intel
                    CherryTrail tablets
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: russianneuromancer at ya.ru
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 144739
  --> https://bugs.freedesktop.org/attachment.cgi?id=144739&action=edit
drm-tip dmesg with drm.debug=0x1e from Irbis TW90

Hello!

I find that backlight is flicker after suspend on certain Intel CherryTrail
tablets. In particular, I reproduced this issue on Irbis TW90 and Lenovo Miix
320-10ICR. There is few ways of reproducing this issue, none is 100% reliable,
but in general it boiling down to several suspend/wakeup cycles for a period of
few hours. In attached Irbis TW90 log issue happened after two suspend/wakeup
cycles, every suspend lasted for a ~3 hours. 

Other symptoms: 
1. When backlight flicker occur brightness adjustment to 10-20% level makes
screen completely black (backlight is disabled). This doesn't happen before
suspend.
2. When backlight flicker occur brightness adjustment to 100% allow to
temporary workaround issue at cost of battery time.
3. Reboot or power cycle usually doesn't help. When backlight flicker started
it continue to happen everywhere, even in BIOS.

Logs from drm-tip/2019-07-05 (ad5a0afdd20635e644d13406e1d1a7ec44398e0e) with
drm.debug=0x1e from both devices is attached.

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