drm/i915: avoid brightness overflow when doing scale
Some card's max brightness level is pretty large, e.g. on Acer Aspire
4732Z, the max level is 989910. If user space set a large enough level
then the current scale done in intel_panel_set_backlight will cause an
integer overflow and the scaled level will be mistakenly small, leaving
user with an almost black screen. This patch fixes this problem.
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
[danvet: Add a comment to explain what's going on.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 67e2c1f..5063ead 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -497,8 +497,11 @@
goto out;
}
- /* scale to hardware */
- level = level * freq / max;
+ /* scale to hardware, but be careful to not overflow */
+ if (freq < max)
+ level = level * freq / max;
+ else
+ level = freq / max * level;
dev_priv->backlight.level = level;
if (dev_priv->backlight.device)