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Diffstat (limited to 'drivers/gpu/drm/i915/intel_panel.c')
-rw-r--r--drivers/gpu/drm/i915/intel_panel.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index e18b3f49074c..b001c90312e7 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1094,12 +1094,25 @@ 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)
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