linux-kernel - Problem: screen partially garbled in i830m (regression)

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Message-ID: <46E7D5AD.7040605@laga.ath.cx>
Date:	Wed, 12 Sep 2007 14:03:57 +0200
From:	Michael Haas <laga@...a.ath.cx>
To:	linux-kernel@...r.kernel.org
CC:	airlied@...ux.ie
Subject: Problem: screen partially garbled in i830m (regression)

Hello list,

I sent this mail to David Airlie two weeks ago but I haven't gotten a
reply so far, that's why I'm posting to LKML this time.  Short summary:
874808c6dd429f7431b906a32c7f78a68e7636af broke intel_agp.ko for me, I'm
getting a garbled screen.

--------------------------------

Hello David,

with recent kernels, there seems to be a problem with agpgart for my
i830m chipset. The upper part of the screen is garbled, e.g. I can make
out parts of the image that is to be displayed, but it's chopped and
repeated. The box with which I'm having this problem is a not a regular
PC, but a x86-based set top box called S100. It's got a fanless Celeron
733 MHz and 128M RAM and it's somewhat popular due to its cheapness.
Just makes a nice living-room computer :)  I'll attach the output of
lspci -vvv.
FYI, I'm not using the official X.org driver but its IEGD counterpart.
Unfortunately, the S100 comes with a TV-out encoder chip that's only
supported by their closed source driver. Since the kernel is not tainted
by that, it shouldn't be a problem - similar problems also occur with
X.org drivers.

With working kernels, I'd get the following messages in dmesg:

<--snip-->
[   40.188375] agpgart: Detected an Intel 830M Chipset.
[   40.188741] agpgart: Detected 380K stolen memory.
[   40.199908] agpgart: AGP aperture is 128M @ 0xf0000000
<--snap-->

A broken kernel will result in the following messages:

<--snip-->
Jul 25 16:29:42 mythbuntu-alpha2 kernel: [   44.941473] Linux agpgart
interface v0.102 (c) Dave Jones
Jul 25 16:29:42 mythbuntu-alpha2 kernel: [   44.957021] agpgart:
Detected an Intel 830M Chipset.
Jul 25 16:29:42 mythbuntu-alpha2 kernel: [   44.957605] agpgart: No
pre-allocated video memory detected.
Jul 25 16:29:42 mythbuntu-alpha2 kernel: [   44.968696] agpgart: AGP
aperture is 128M @ 0xf0000000
<--snap-->

I used git-bisect to narrow down change that introduced this problem and
came up with this:

<--snip-->

874808c6dd429f7431b906a32c7f78a68e7636af is first bad commit
commit 874808c6dd429f7431b906a32c7f78a68e7636af
Author: Wang Zhenyu <zhenyu.z.wang@...el.com>
Date:   Wed Jun 6 11:16:25 2007 +0800

  [AGPGART] intel_agp: Add support for G33, Q33 and Q35 chipsets

  This patch adds pci ids for G33, Q33 and Q35 chips, and update with new
  GTT size and stolen mem size detect method on these chips.

  Signed-off-by: Wang Zhenyu <zhenyu.z.wang@...el.com>
  Signed-off-by: Dave Jones <davej@...hat.com>

:040000 040000 39b18b6860f139cb28a80020dc9347314753e16d
da24fb8672087cdfe6509cd1d4cb189534f887d6 M  drivers
<--snap-->

Particulary, there's a change to agp.h:

<--snip-->
-#define I830_GMCH_GMS_MASK  0x70
+#define I830_GMCH_GMS_MASK  0xF0
<--snap-->

I reverted this change in my git tree and I'm now running
2.6.23-rc3-gb377fd39-dirty without any distortion at all. Do you think
this can be fixed? I'll be glad to provide more Information. Thank you
for your time!

Regards,

Michael

View attachment "lspci-verbose.txt" of type "text/plain" (7864 bytes)