From 22505b82a2800bddb67908522833bef96dd15845 Mon Sep 17 00:00:00 2001 From: Aaron Lu Date: Fri, 2 Aug 2013 09:16:03 +0800 Subject: [PATCH] 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 --- drivers/gpu/drm/i915/intel_panel.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) 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) -- 2.20.1