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Backlight flicker after suspend on certain Intel CherryTrail tablets

Submitted by RussianNeuroMancer @RussianNeuroMancer

Assigned to Intel GFX Bugs mailing list

Link to original bug (#111095)

Description

Created attachment 144739
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.

**Attachment 144739**, "drm-tip dmesg with drm.debug=0x1e from Irbis TW90":
dmesg_tw90
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