[Bug 106181] Laptop with i915 GPU hangs changing screen brightness with kernel 4.16.x, 4.15 fine.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106181

Öyvind Saether <oyvinds at everdot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |NOTOURBUG

--- Comment #1 from Öyvind Saether <oyvinds at everdot.org> ---
Further investigation and testing on this laptop with Fedora 4.16.2 and 4.16.4
and comparing configurations with 4.15.17 reveals that this Fedora
configuration change is the cause:

< CONFIG_SATA_MOBILE_LPM_POLICY=0
> CONFIG_SATA_MOBILE_LPM_POLICY=3

which can be fixed by adding this kernel boot parameter:

ahci.mobile_lpm_policy=1

(I guess 0 would work to, but
/sys/class/scsi_host/host*/link_power_management_policy was set to
max_performance with 0 on 4.15.17)

One Obvious Question: Why would having this set to 3 (med_power_with_dipm) make
the laptop hang immediately when changing the Screen Brightness manually (or
when redshift is running)? This seems counterintuitive and very very strange.

I can reproduce this 100%. I can even do this on 4.15.17,
for powercontrol in /sys/class/scsi_host/host*/link_power_management_policy ;
do
  echo 'min_powermin_power' > $powercontrol
done
and make that one hang by changing the screen brightness. I do not understand.

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