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The current code does not follow Intel documentation: It misses some things and does other, undocumented things. This causes wrong backlight values in certain conditions. Instead of adding tricky code handling badly documented and rare corner cases, don't handle combination mode specially at all. This way PCI_LBPC is never touched and weird things shouldn't happen. If combination mode is enabled, then the only downside is that changing the brightness has a greater granularity (the LBPC value), but LBPC is at most 254 and the maximum is in the thousands, so this is no real functional loss. A potential problem with not handling combined mode is that a brightness of max * PCI_LBPC is not bright enough. However, this is very unlikely because from the documentation LBPC seems to act as a scaling factor and doesn't look like it's supposed to be changed after boot. The value at boot should always result in a bright enough screen. IMPORTANT: However, although usually the above is true, it may not be when people ran an older (2.6.37) kernel which messed up the LBPC register, and they are unlucky enough to have a BIOS that saves and restores the LBPC value. Then a good kernel may seem to not work: Max brightness isn't bright enough. If this happens people should boot back into the old kernel, set brightness to the maximum, and then reboot. After that everything should be fine. For more information see the below links. This fixes bugs: http://bugzilla.kernel.org/show_bug.cgi?id=23472 http://bugzilla.kernel.org/show_bug.cgi?id=25072 Signed-off-by: Indan Zupancic <indan@nul.nu> Tested-by: Alex Riesen <raa.lkml@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
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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