From: Jani Nikula Date: Wed, 5 Nov 2014 12:46:31 +0000 (+0200) Subject: drm/i915: safeguard against too high minimum brightness X-Git-Tag: v4.14-rc1~6479^2~5^2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=e1c412e75754ab7b7002f3e18a2652d999c40d4b;p=platform%2Fkernel%2Flinux-rpi.git drm/i915: safeguard against too high minimum brightness Never trust (your interpretation of) the VBT. Regression from commit 6dda730e55f412a6dfb181cae6784822ba463847 Author: Jani Nikula Date: Tue Jun 24 18:27:40 2014 +0300 drm/i915: respect the VBT minimum backlight brightness causing div by zero if VBT minimum brightness equals maximum brightness. Despite my attempts I've failed in my detective work to figure out what the root cause is. This is not the real fix, but we have to do something. Reported-by: Mike Auty Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86551 Cc: stable@vger.kernel.org (v3.17+) Reviewed-by: Daniel Vetter Signed-off-by: Jani Nikula --- diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index 0e018cb..41b3be2 100644 --- a/drivers/gpu/drm/i915/intel_panel.c +++ b/drivers/gpu/drm/i915/intel_panel.c @@ -1098,12 +1098,25 @@ static u32 get_backlight_min_vbt(struct intel_connector *connector) struct drm_device *dev = connector->base.dev; struct drm_i915_private *dev_priv = dev->dev_private; struct intel_panel *panel = &connector->panel; + int min; WARN_ON(panel->backlight.max == 0); + /* + * XXX: If the vbt value is 255, it makes min equal to max, which leads + * to problems. There are such machines out there. Either our + * interpretation is wrong or the vbt has bogus data. Or both. Safeguard + * against this by letting the minimum be at most (arbitrarily chosen) + * 25% of the max. + */ + min = clamp_t(int, dev_priv->vbt.backlight.min_brightness, 0, 64); + if (min != dev_priv->vbt.backlight.min_brightness) { + DRM_DEBUG_KMS("clamping VBT min backlight %d/255 to %d/255\n", + dev_priv->vbt.backlight.min_brightness, min); + } + /* vbt value is a coefficient in range [0..255] */ - return scale(dev_priv->vbt.backlight.min_brightness, 0, 255, - 0, panel->backlight.max); + return scale(min, 0, 255, 0, panel->backlight.max); } static int bdw_setup_backlight(struct intel_connector *connector)