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drm/i915: avoid brightness overflow when doing scale

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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>
This commit is contained in:
Aaron Lu 2013-08-02 09:16:03 +08:00 committed by Daniel Vetter
parent 9dbd8febb4
commit 22505b82a2
1 changed files with 5 additions and 2 deletions
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7
drivers/gpu/drm/i915/intel_panel.c
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@ -497,8 +497,11 @@ void intel_panel_set_backlight(struct drm_device *dev, u32 level, u32 max)
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)