This is a note to let you know that I've just added the patch titled
drm/i915: safeguard against too high minimum brightness
to the 3.17-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-safeguard-against-too-high-minimum-brightness.patch
and it can be found in the queue-3.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e1c412e75754ab7b7002f3e18a2652d999c40d4b Mon Sep 17 00:00:00 2001
From: Jani Nikula <jani.nikula@xxxxxxxxx>
Date: Wed, 5 Nov 2014 14:46:31 +0200
Subject: drm/i915: safeguard against too high minimum brightness
From: Jani Nikula <jani.nikula@xxxxxxxxx>
commit e1c412e75754ab7b7002f3e18a2652d999c40d4b upstream.
Never trust (your interpretation of) the VBT. Regression from
commit 6dda730e55f412a6dfb181cae6784822ba463847
Author: Jani Nikula <jani.nikula@xxxxxxxxx>
Date: Tue Jun 24 18:27:40 2014 +0300
drm/i915: respect the VBT minimum backlight brightness
causing div by zero if VBT minimum brightness equals maximum brightness.
Despite my attempts I've failed in my detective work to figure out what
the root cause is. This is not the real fix, but we have to do
something.
Reported-by: Mike Auty <mike.auty@xxxxxxxxx>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86551
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_panel.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1074,12 +1074,25 @@ static u32 get_backlight_min_vbt(struct
struct drm_device *dev = connector->base.dev;
struct drm_i915_private *dev_priv = dev->dev_private;
struct intel_panel *panel = &connector->panel;
+ int min;
WARN_ON(panel->backlight.max == 0);
+ /*
+ * XXX: If the vbt value is 255, it makes min equal to max, which leads
+ * to problems. There are such machines out there. Either our
+ * interpretation is wrong or the vbt has bogus data. Or both. Safeguard
+ * against this by letting the minimum be at most (arbitrarily chosen)
+ * 25% of the max.
+ */
+ min = clamp_t(int, dev_priv->vbt.backlight.min_brightness, 0, 64);
+ if (min != dev_priv->vbt.backlight.min_brightness) {
+ DRM_DEBUG_KMS("clamping VBT min backlight %d/255 to %d/255\n",
+ dev_priv->vbt.backlight.min_brightness, min);
+ }
+
/* vbt value is a coefficient in range [0..255] */
- return scale(dev_priv->vbt.backlight.min_brightness, 0, 255,
- 0, panel->backlight.max);
+ return scale(min, 0, 255, 0, panel->backlight.max);
}
static int bdw_setup_backlight(struct intel_connector *connector)
Patches currently in stable-queue which might be from jani.nikula@xxxxxxxxx are
queue-3.17/drm-i915-disable-caches-for-global-gtt.patch
queue-3.17/drm-i915-safeguard-against-too-high-minimum-brightness.patch
queue-3.17/drm-i915-dp-only-use-training-pattern-3-on-platforms-that-support-it.patch
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