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=23472http://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>
... and not if the maximum is non-zero. This fixes the typo introduced
in 47356eb672 and preserves the backlight value from boot.
[ickle: My thanks also to Indan Zupancic for diagnosing the original
regression and suggesting the appropriate fix.]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org # after 47356eb672
By tracking the current status of the backlight we can prevent recording
the value of the current backlight when we have disabled it. And so
prevent restoring it to 'off' after an unbalanced sequence of
intel_lvds_disable/enable.
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=22672
Tested-by: Alex Riesen <raa.lkml@gmail.com>
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
After a GPU reset, the backlight controller registers may be also reset
to 0. In that case we should restore those to the original values
programmed by the BIOS. Note that we still lack the code to handle the
case where the BIOS failed to program those registers at all...
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
There were two instances of code to control the panel backlight and
neither handled the complete set of device variations.
Fixes:
Bug 29716 - [GM965] Regression: Backlight resets to minimum when changing resolution
https://bugs.freedesktop.org/show_bug.cgi?id=29716
And a bug on one of my PineView boxes which overflowed the backlight
value.
Incorporates part of a similar patch by Matthew Garrett that exposes a
native Intel backlight controller.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
v2: Hook in DP paths to keep FULLSCREEN panel fitting on eDP.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Indan Zupancic