On Wed, Nov 05, 2014 at 02:46:31PM +0200, Jani Nikula wrote: > Never trust (your interpretation of) the VBT. Regression from > > commit 6dda730e55f412a6dfb181cae6784822ba463847 > Author: Jani Nikula <jani.nikula@xxxxxxxxx> > 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 <mike.auty@xxxxxxxxx> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86551 > Cc: stable@xxxxxxxxxxxxxxx (v3.17+) > Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_panel.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index e18b3f49074c..b001c90312e7 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -1094,12 +1094,25 @@ 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); min_brightness is unsigned everywhere I've look, so a min_t looks sufficient here. Otherwise Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Also, more gin pls :( -Daniel > + 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) > -- > 2.1.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
