Hi,
I've noticed that v3.14 breaks the backlight on Dell XPS13. Reverting the
following commit fixes the issue for me (i.e. the GUI brightness controls work
again):
bc0bb9fd1c78 drm/i915: remove QUIRK_NO_PCH_PWM_ENABLE
It appears that in v3.14 (with the above patch):
* intel_backlight/brightness=4882 (max & default) causes
acpi_video0/brightness to have no effect.
* intel_backlight/brightness=0 causes acpi_video0/brightness to behave
corrrectly (the firmware (I assume) fades the brightness gradually when
acpi_video0/brightness is set)
* intel_backlight/brightness=something else in between often causes
acpi_video0 and intel_backlight to apparently "fight" over the backlight,
resulting in brightness flickering up and down every second or so.
Reverting the above patch on v3.14:
* intel_backlight/brightness has no effect
* acpi_video0/brightness works normally
It doesn't seem quite as simple as them trying to use the same hardware since
when intel_backlight/brightness=4882, acpi_video0/brightness has no effect at
all, so I don't really get what's going on.
Can anybody shed some light or suggest a proper fix for this recurring issue?
Thanks
James
On Thu, 03 Apr 2014, James Hogan <[email protected]> wrote:
> Hi,
>
> I've noticed that v3.14 breaks the backlight on Dell XPS13. Reverting the
> following commit fixes the issue for me (i.e. the GUI brightness controls work
> again):
>
> bc0bb9fd1c78 drm/i915: remove QUIRK_NO_PCH_PWM_ENABLE
>
> It appears that in v3.14 (with the above patch):
> * intel_backlight/brightness=4882 (max & default) causes
> acpi_video0/brightness to have no effect.
> * intel_backlight/brightness=0 causes acpi_video0/brightness to behave
> corrrectly (the firmware (I assume) fades the brightness gradually when
> acpi_video0/brightness is set)
> * intel_backlight/brightness=something else in between often causes
> acpi_video0 and intel_backlight to apparently "fight" over the backlight,
> resulting in brightness flickering up and down every second or so.
>
> Reverting the above patch on v3.14:
> * intel_backlight/brightness has no effect
> * acpi_video0/brightness works normally
>
> It doesn't seem quite as simple as them trying to use the same hardware since
> when intel_backlight/brightness=4882, acpi_video0/brightness has no effect at
> all, so I don't really get what's going on.
>
> Can anybody shed some light or suggest a proper fix for this recurring issue?
Tracked at https://bugs.freedesktop.org/show_bug.cgi?id=76276
BR,
Jani.
>
> Thanks
> James
--
Jani Nikula, Intel Open Source Technology Center