Merge tag 'pinctrl-v3.19-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw...

[cascardo/linux.git] / drivers / gpu / drm / i915 / intel_panel.c

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 0e018cb..41b3be2 100644 (file)
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -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)