Commit 22505b82 authored Aug 02, 2013 by Aaron Lu Committed by Daniel Vetter Aug 07, 2013

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>

parent 9dbd8feb

drivers/gpu/drm/i915/intel_panel.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -497,8 +497,11 @@ void intel_panel_set_backlight(struct drm_device *dev, u32 level, u32 max)
		goto out;
		}

		/* scale to hardware */
		/* 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)