This is a note to let you know that I've just added the patch titled
drm/i915: try not to lose backlight CBLV precision
to the 3.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-i915-try-not-to-lose-backlight-cblv-precision.patch
and it can be found in the queue-3.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From cac6a5ae0118832936eb162ec4cedb30f2422bcc Mon Sep 17 00:00:00 2001
From: Jani Nikula <jani.nikula@xxxxxxxxx>
Date: Fri, 23 Aug 2013 10:50:39 +0300
Subject: drm/i915: try not to lose backlight CBLV precision
From: Jani Nikula <jani.nikula@xxxxxxxxx>
commit cac6a5ae0118832936eb162ec4cedb30f2422bcc upstream.
ACPI has _BCM and _BQC methods to set and query the backlight
brightness, respectively. The ACPI opregion has variables BCLP and CBLV
to hold the requested and current backlight brightness, respectively.
The BCLP variable has range 0..255 while the others have range
0..100. This means the _BCM method has to scale the brightness for BCLP,
and the gfx driver has to scale the requested value back for CBLV. If
the _BQC method uses the CBLV variable (apparently some implementations
do, some don't) for current backlight level reporting, there's room for
rounding errors.
Use DIV_ROUND_UP for scaling back to CBLV to get back to the same values
that were passed to _BCM, presuming the _BCM simply uses bclp = (in *
255) / 100 for scaling to BCLP.
Reference: https://gist.github.com/aaronlu/6314920
Reported-by: Aaron Lu <aaron.lu@xxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Reviewed-by: Aaron Lu <aaron.lu@xxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_opregion.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/gpu/drm/i915/intel_opregion.c
+++ b/drivers/gpu/drm/i915/intel_opregion.c
@@ -173,7 +173,7 @@ static u32 asle_set_backlight(struct drm
return ASLE_BACKLIGHT_FAILED;
intel_panel_set_backlight(dev, bclp, 255);
- iowrite32((bclp*0x64)/0xff | ASLE_CBLV_VALID, &asle->cblv);
+ iowrite32(DIV_ROUND_UP(bclp * 100, 255) | ASLE_CBLV_VALID, &asle->cblv);
return 0;
}
Patches currently in stable-queue which might be from jani.nikula@xxxxxxxxx are
queue-3.11/drm-i915-try-not-to-lose-backlight-cblv-precision.patch
queue-3.11/drm-i915-do-not-update-cursor-in-crtc-mode-set.patch
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