Bug 42839 - drm/i915: wrong fifo size due to uncareful refactoring which results in an xserver crash at 800x600
Summary: drm/i915: wrong fifo size due to uncareful refactoring which results in an xs...
Status: RESOLVED CODE_FIX
Alias: None
Product: Drivers
Classification: Unclassified
Component: Video(DRI - Intel) (show other bugs)
Hardware: All Linux
: P1 normal
Assignee: drivers_video-dri-intel@kernel-bugs.osdl.org
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2012-02-29 13:08 UTC by Lukas Anzinger
Modified: 2012-06-26 04:16 UTC (History)
2 users (show)

See Also:
Kernel Version: 2.6.33.20
Subsystem:
Regression: Yes
Bisected commit-id:

Attachments
Fix wrong fifo size regression (789 bytes, patch)
2012-02-29 13:08 UTC, Lukas Anzinger 		Details | Diff
Add an attachment (proposed patch, testcase, etc.)

Description Lukas Anzinger 2012-02-29 13:08:21 UTC 
Created attachment 72498 [details]
Fix wrong fifo size regression

Hi,

I've encountered a nasty bug in the drm/i915 part of Debian's stable kernel. The code is also present in 2.6.33.20, which is the latest stable upstream release of 2.6.33.y at the time of writing.

During a refactoring of the i915 driver a regression has been introduced (commit e70236a8d3d0a4c100a0b9f7d394d9bda9c56aca): For some chipsets the wrong fifo size is determined which results in lot's of pixel errors when starting the xserver and choosing 800x600 as a resolution. If another resolution is used (eg. 1024x768 or 1280x1024), I don't encounter this problem.

I've attached a patch that fixes the problem (no pixel errors anymore) and determines the correct fifo size.

Regards,

Lukas
Comment 1 Chris Wilson 2012-02-29 14:21:20 UTC 
commit 8f4695ed1c9e068772bcce4cd4ff03f88d57a008
Author: Adam Jackson <ajax@redhat.com>
Date:   Fri Apr 16 18:20:57 2010 -0400

    drm/i915: Attempt to fix watermark setup on 85x (v2)
    
    IS_MOBILE() catches 85x, so we'd always try to use the 9xx FIFO sizing;
    since there's an explicit 85x version, this seems wrong.
    
    v2: Handle 830m correctly too.
    
    Signed-off-by: Adam Jackson <ajax@redhat.com>
    Reviewed-by: Eric Anholt <eric@anholt.net>
    Signed-off-by: Eric Anholt <eric@anholt.net>

Please test that and then send it to stable@kernel.org, adding your Reported-and-tested-by and Bugzilla reference.
Comment 2 Lukas Anzinger 2012-03-02 11:56:51 UTC 
Hi,

looks good to me. I opt for inclusion in the 2.6.33.y branch.

Regards,

Lukas
Comment 3 Jonathan Nieder 2012-06-26 04:16:21 UTC 
References: http://bugs.debian.org/661696
Note You need to log in before you can comment on or make changes to this bug.