On Wed, Apr 09, 2014 at 01:35:35PM +0300, Jani Nikula wrote: > Some machines use an external EC for controlling the backlight. Info > about this is present in the VBT. Do not setup native backlight control > if no PWM backlight is available or supported according to VBT. The > acpi_backlight interface appears to work for the EC control. > > In most cases there has been no harm done, but it looks like there are > machines out there that have both an EC and our PWM line connected to > the same wire. This, obviously, does not end well. > > This should fix the regression caused by > commit bc0bb9fd1c7810407ab810d204bbaecb255fddde > Author: Jani Nikula <jani.nikula@xxxxxxxxx> > Date: Thu Nov 14 12:14:29 2013 +0200 > > drm/i915: remove QUIRK_NO_PCH_PWM_ENABLE > > AFAICT the quirk removed by the above commit effectively resulted in > i915 not driving the backlight PWM output, thus not messing things up. > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76276 > Reference: https://bugzilla.kernel.org/show_bug.cgi?id=47941 > CC: Aaron Lu <aaron.lu@xxxxxxxxx> > CC: Kamal Mostafa <kamal@xxxxxxxxxxxxx> > CC: Eric Griffith <EGriffith92@xxxxxxxxx> > CC: Kent Baxley <kent.baxley@xxxxxxxxxxxxx> > CC: stable@xxxxxxxxxxxxxxx [v3.14+] Imo this part is a bit frisky - if we get positive testing on the xps13 machines I'd shovel this into 3.15-fixes and then resurrect the old hack for stable kernels. Imo this is risky enough that we should attempt to backport it before 3.15 is actually released. -Daniel > Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_panel.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index cb058408c70e..0eead16aeda7 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -1065,6 +1065,11 @@ int intel_panel_setup_backlight(struct drm_connector *connector) > unsigned long flags; > int ret; > > + if (!dev_priv->vbt.backlight.present) { > + DRM_DEBUG_KMS("native backlight control not available per VBT\n"); > + return 0; > + } > + > /* set level and max in panel struct */ > spin_lock_irqsave(&dev_priv->backlight_lock, flags); > ret = dev_priv->display.setup_backlight(intel_connector); > -- > 1.7.9.5 > > _______________________________________________ > 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html