linux-kernel - Re: i915: wrong framebuffer size in 2.6.36-rc3

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Message-ID: <87hbiccj3r.fsf@turtle.gmx.de>
Date:	Mon, 30 Aug 2010 15:42:32 +0200
From:	Sven Joachim <svenjoac@....de>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Ivan Bulatovic <combuster@....com>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Eric Anholt <eric@...olt.net>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: i915: wrong framebuffer size in 2.6.36-rc3

On 2010-08-30 11:57 +0200, Pekka Enberg wrote:

> On Mon, Aug 30, 2010 at 12:36 PM, Sven Joachim <svenjoac@....de> wrote:
>> On my laptop which has a 1280x800 display, only the upper left 848x480
>> pixels are used on the console in 2.6.36-rc3.  The resolution is
>> correct, but /sys/class/graphics/fb0/modes looks like this:
>>
>> U:848x480p-0
>>
>> This is a regression from 2.6.35.  The graphics card according to lspci:
>>
>> 00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS,
>> 943/940GML Express Integrated Graphics Controller (rev 03)
>
> Yeah, you're not alone on this:
>
> http://lkml.org/lkml/2010/8/23/452

Incidentally, I did not notice the problem initially described in this
thread, and 2.6.36-rc2 actually seems OK for me.  But after this commit:

commit 9559fcdbff4f93d29af04478bbc48294519424f5
Author: Jesse Barnes <jbarnes@...tuousgeek.org>
Date:   Tue Aug 24 11:31:16 2010 -0700

    drm/i915: fix vblank wait test condition
    
    When converting this to the new wait_for macro I inverted the wait
    condition, which causes all sorts of problems.  So correct it to fix
    several failures caused by the bad wait (flickering, bad output
    detection, tearing, etc.).
    
    Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
    Tested-by: Sitsofe Wheeler <sitsofe@...oo.com>
    Signed-off-by: Jesse Barnes <jbarnes@...tuousgeek.org>
    Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

@ -992,7 +992,7 @@ void intel_wait_for_vblank(struct drm_device *dev, int pipe)
 
 	/* Wait for vblank interrupt bit to set */
 	if (wait_for((I915_READ(pipestat_reg) &
-		      PIPE_VBLANK_INTERRUPT_STATUS) == 0,
+		      PIPE_VBLANK_INTERRUPT_STATUS),
 		     50, 0))
 		DRM_DEBUG_KMS("vblank wait timed out\n");
 }


only the upper left 848x480 pixels of the display are used for the
framebuffer.  Booting with the video=1280x800 commandline option works
around this problem.

Sven
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