Re: [PATCH] Revert "drm/i915: write backlight harder"

From: Takashi Iwai <tiwai@suse.de>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@intel.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH] Revert "drm/i915: write backlight harder"
Date: Fri, 22 Mar 2013 16:06:14 +0100	[thread overview]
Message-ID: <s5hehf7a2zd.wl%tiwai@suse.de> (raw)
In-Reply-To: <1363963486-7891-1-git-send-email-daniel.vetter@ffwll.ch>

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@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@intel.com>
> Cc: Takashi Iwai <tiwai@suse.de>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Feel free to add my tested-by tags to all three.

  Tested-by: Takashi Iwai <tiwai@suse.de>

thanks,

Takashi