[stable] PATCH drm/i915/lvds: ditch ->prepare special case

[Brad Figg]

On 08/14/2013 07:44 AM, Haitao Zhang wrote:
> This commit fixed the following bug:
> 
> https://bugs.launchpad.net/ubuntu/quantal/+source/linux/+bug/1103856
> 
> originally affected on Thinkpad M490s laptop with v3.2 kernel,
> the patch also applicable on v3.2.50, v3.4.57 stable kernel and 
> 3.5.y.z extended stable kernel, since it was merged into v3.6 kernel officially.
> the test was based on Ironlake laptop Thinkpad v490s and 
> pre-Ironlake laptop Thinkpad X200 with all the stable kernel listed above.
> 
> 
> commit 520c41cf2fa029d1e8b923ac2026f96664f17c4b
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date:   Wed Jul 11 16:27:52 2012 +0200
> 
>     drm/i915/lvds: ditch ->prepare special case
>     
>     LVDS is the first output where dpms on/off and prepare/commit don't
>     perfectly match. Now the idea behind this special case seems to be
>     that for simple resolution changes on the LVDS we don't need to stop
>     the pipe, because (at least on newer chips) we can adjust the panel
>     fitter on the fly.
>     
>     There are a few problems with the current code though:
>     - We still stop and restart the pipe unconditionally, because the
> crtc
>       helper code isn't flexible enough.
>     - We show some ugly flickering, especially when changing crtcs (this
>       the crtc helper would actually take into account, but we don't
>       implement the encoder->get_crtc callback required to make this
> work
>       properly).
>     
>     So it doesn't even work as advertised. I agree that it would be nice
>     to do resolution changes on LVDS (and also eDP) whithout blacking
> the
>     screen where the panel fitter allows to do that. But imo we should
>     implement this as a special case a few layers up in the mode set
> code,
>     akin to how we already detect simple framebuffer changes (and only
>     update the required registers with ->mode_set_base).
>     
>     Until this is all in place, make our lives easier and just rip it
> out.
>     
>     Also note that this seems to fix actual bugs with enabling the lvds
>     output, see:
>     
> 
> http://lists.freedesktop.org/archives/intel-gfx/2012-July/018614.html
>     
>     Cc: Takashi Iwai <tiwai at suse.de>
>     Cc: Giacomo Comes <comes at naic.edu>
>     Acked-by: Chris Wilson <chris at chris-wilson.co.uk>
>     Tested-by: Takashi Iwai <tiwai at suse.de>
>     Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> 
> 

Haitao,

When submitting patches to the Ubuntu kernel team mailing list we like
the subject line to be in a format that helps us understand where you want
your patch/patches applied. Please refer to:
     https://wiki.ubuntu.com/Kernel/Dev/StablePatchFormat

Also, bug task status should not be "Fix Committed" until it has been applied
to the relevant ubuntu git repository.

Thanks,
Brad
-- 
Brad Figg brad.figg at canonical.com http://www.canonical.com