[Bug 111293] [chv][regression][bisected] Brightness adjustment on Lenovo Miix 320-10ICR and Lenovo Miix2 8 is broken since Linux 5.3rc1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111293

--- Comment #5 from russianneuromancer at ya.ru ---
Created attachment 144959
  --> https://bugs.freedesktop.org/attachment.cgi?id=144959&action=edit
drm-tip dmesg with drm.debug=0x1e from Lenovo Miix2 8

As I just found same issue is reproducible on Lenovo Miix2 8 too.

Attached log is from drm-tip 2019-08-05
(2bb7df95d4e058e61d9de39f1b97404592708d24)

> If the acpi driver exposed a /sys/class/backlight, xf86-video-intel should have still found it.

Lenovo Miix2 8, Lenovo Miix 320-10IRC
On Linux 5.2 there is just one intel_backlight, adjusting brightness via
intel_backlight works.

Lenovo Miix2 8:
On Linux 5.3 there is acpi_video0 and acpi_video1, echo values to brightness
file in each one doesn't change backlight level.

Lenovo Miix 320-10IRC:
On Linux 5.3 there is...

~# ls /sys/class/backlight
acpi_video0  acpi_video1  acpi_video2  acpi_video3  acpi_video4  acpi_video5 
acpi_video6  acpi_video7

As with Lenovo Miix2 8, echo values to brightness file in each acpi_video
doesn't change backlight level.

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