From: Aaron Lu Date: Fri, 2 Aug 2013 01:16:03 +0000 (+0800) Subject: drm/i915: avoid brightness overflow when doing scale X-Git-Url: https://rtime.felk.cvut.cz/gitweb/linux-imx.git/commitdiff_plain/22505b82a2800bddb67908522833bef96dd15845 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 [danvet: Add a comment to explain what's going on.] Signed-off-by: Daniel Vetter --- diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index 67e2c1f1c9a8..5063eadac3ef 100644 --- a/drivers/gpu/drm/i915/intel_panel.c +++ b/drivers/gpu/drm/i915/intel_panel.c @@ -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)