mirror of
https://github.com/hardkernel/linux.git
synced 2026-05-21 03:19:04 +09:00
5d031e5b63
This is a revert of 6aa56062ea.
This was originally introduced to workaround reads of the ringbuffer
registers returning 0 on SandyBridge causing hangs due to ringbuffer
overflow. The root cause here was reads through the GT powerwell require
the forcewake dance, something we only learnt of later. Now it appears
that reading the reported head position from the HWS is returning
garbage, leading once again to hangs.
For example, on q35 the autoreported head reports:
[ 217.975608] head now 00010000, actual 00010000
[ 436.725613] head now 00200000, actual 00200000
[ 462.956033] head now 00210000, actual 00210010
[ 485.501409] head now 00400000, actual 00400020
[ 508.064280] head now 00410000, actual 00410000
[ 530.576078] head now 00600000, actual 00600020
[ 553.273489] head now 00610000, actual 00610018
which appears reasonably sane. In contrast, if we look at snb:
[ 141.970680] head now 00e10000, actual 00008238
[ 141.974062] head now 02734000, actual 000083c8
[ 141.974425] head now 00e10000, actual 00008488
[ 141.980374] head now 032b5000, actual 000088b8
[ 141.980885] head now 03271000, actual 00008950
[ 142.040628] head now 02101000, actual 00008b40
[ 142.180173] head now 02734000, actual 00009050
[ 142.181090] head now 00000000, actual 00000ae0
[ 142.183737] head now 02734000, actual 00009050
In addition, the automatic reporting of the head position is scheduled
to be defeatured in the future. It has no more utility, remove it.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45492
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
************************************************************
* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
************************************************************
The Direct Rendering Manager (drm) is a device-independent kernel-level
device driver that provides support for the XFree86 Direct Rendering
Infrastructure (DRI).
The DRM supports the Direct Rendering Infrastructure (DRI) in four major
ways:
1. The DRM provides synchronized access to the graphics hardware via
the use of an optimized two-tiered lock.
2. The DRM enforces the DRI security policy for access to the graphics
hardware by only allowing authenticated X11 clients access to
restricted regions of memory.
3. The DRM provides a generic DMA engine, complete with multiple
queues and the ability to detect the need for an OpenGL context
switch.
4. The DRM is extensible via the use of small device-specific modules
that rely extensively on the API exported by the DRM module.
Documentation on the DRI is available from:
http://dri.freedesktop.org/wiki/Documentation
http://sourceforge.net/project/showfiles.php?group_id=387
http://dri.sourceforge.net/doc/
For specific information about kernel-level support, see:
The Direct Rendering Manager, Kernel Support for the Direct Rendering
Infrastructure
http://dri.sourceforge.net/doc/drm_low_level.html
Hardware Locking for the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/hardware_locking_low_level.html
A Security Analysis of the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/security_low_level.html