[Intel-gfx] [PATCH] Revert "drm/i915: write backlight harder"

[Daniel Vetter]

On Fri, Mar 22, 2013 at 04:06:14PM +0100, Takashi Iwai wrote:
> At Fri, 22 Mar 2013 15:44:46 +0100,
> Daniel Vetter wrote:
> > 
> > This reverts commit cf0a6584aa6d382f802f2c3cacac23ccbccde0cd.
> > 
> > Turns out that cargo-culting breaks systems. Note that we can't revert
> > further, since
> > 
> > commit 770c12312ad617172b1a65b911d3e6564fc5aca8
> > Author: Takashi Iwai <tiwai at suse.de>
> > Date:   Sat Aug 11 08:56:42 2012 +0200
> > 
> >     drm/i915: Fix blank panel at reopening lid
> > 
> > fixed a regression in 3.6-rc kernels for which we've never figured out
> > the exact root cause. But some further inspection of the backlight
> > code reveals that it's seriously lacking locking. And especially the
> > asle backlight update is know to get fired (through some smm magic)
> > when writing specific backlight control registers. So the possibility
> > of suffering from races is rather real.
> > 
> > Until those races are fixed I don't think it makes sense to try
> > further hacks. Which sucks a bit, but sometimes that's how it is :(
> > 
> > References: http://www.mail-archive.com/intel-gfx@lists.freedesktop.org/msg18788.html
> > Cc: Jani Nikula <jani.nikula at intel.com>
> > Cc: Takashi Iwai <tiwai at suse.de>
> > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> Feel free to add my tested-by tags to all three.
> 
>   Tested-by: Takashi Iwai <tiwai at suse.de>

Picked up for -fixes with the additional kernel bz link for #47941 added.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch