drm/i915: safeguard against too high minimum brightness
Never trust (your interpretation of) the VBT. Regression from
commit 6dda730e55
Author: Jani Nikula <jani.nikula@intel.com>
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@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86551
Cc: stable@vger.kernel.org (v3.17+)
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
parent
a024d2e6f1
commit
e1c412e757
|
@ -1098,12 +1098,25 @@ static u32 get_backlight_min_vbt(struct intel_connector *connector)
|
|||
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)
|
||||
|
|
Loading…
Reference in a new issue