[Bug 94753] Lockup after display enter powersaving mode

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94753

--- Comment #4 from russianneuromancer at ya.ru ---
Created attachment 123243
  --> https://bugs.freedesktop.org/attachment.cgi?id=123243&action=edit
debug dmesg

> This is one problem:
> [    3.987505] [drm:pwm_setup_backlight [i915]] *ERROR* Failed to own the pwm chip
> and can explain the backlight staying on.
> The best workaround for that right now is to make i915 a module, and build the required i2c/gpio/pwm support into the kernel itself:
> CONFIG_I2C_DESIGNWARE_PLATFORM=y
> CONFIG_I2C_DESIGNWARE_PCI=y
> CONFIG_INTEL_SOC_PMIC=y
> CONFIG_GPIO_CRYSTAL_COVE=y
> CONFIG_PWM_CRC=y
> CONFIG_DRM_I915=m

Unfortunately, I doesn't know how to apply this to kernel, how to compile it,
etc.
Not sure if this related to this particular report at all - isn't this is
separate problem?

> For some further debug information please boot with drm.debug=0xe kernel command line option and attach the dmesg here.
Attached (stock kernel of Ubuntu 16.04 LiveUSB).

> Also please attach a copy of /sys/kernel/debug/dri/0/i915_opregion
Attached above.

> As far as the lockup goes, Jani had a very similar problem on a CHT tablet recently, but I think that turned out to due to wifi.
In my case this is not because of WiFi for sure, there just no drivers for WiFi
of this tablet in kernel right now. So when I boot Ubuntu 16.04 LiveUSB WiFi
just not working, while issue is still reproducible.

> Your log is also full of some audio noise as well, so I'd also try to eliminate as many non-display related drivers as possible.
That right, there two reports about this:
https://bugzilla.kernel.org/show_bug.cgi?id=117141
https://bugzilla.kernel.org/show_bug.cgi?id=115201

> To rule out GPU runtime PM do this:
> 'echo on > /sys/class/drm/card0/device/power/control'
> before turning off the display.
For me 'cat /sys/class/drm/card0/device/power/control' return 'on' right now.
Nevertheless, I tried to 'echo on > /sys/class/drm/card0/device/power/control'
and then tried to reproduce issue using steps I described above - issue is
still reproducible.

> To rule out display power well problems boot with i915.disable_power_well=0 kernel command line option.
I tried to boot with this kernel option, but issue is still reproducible with
disabled power well.

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