From: Jani Nikula <jani.nikula@intel.com>
To: James Hogan <james@albanarts.com>,
Imre Deak <imre.deak@intel.com>,
Kamal Mostafa <kamal@canonical.com>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org
Subject: Re: drm/i915: XPS13 backlight regression in v3.14
Date: Thu, 03 Apr 2014 10:02:58 +0300 [thread overview]
Message-ID: <87zjk2lwt9.fsf@intel.com> (raw)
In-Reply-To: <2613018.1cXJgVWlHm@radagast>
On Thu, 03 Apr 2014, James Hogan <james@albanarts.com> 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
prev parent reply other threads:[~2014-04-03 7:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-03 3:12 drm/i915: XPS13 backlight regression in v3.14 James Hogan
2014-04-03 3:12 ` James Hogan
2014-04-03 7:02 ` Jani Nikula [this message]
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