drm/i915: do not setup backlight if not available according to VBT

jnikula · jnikula · commit c675949ec58c · 2014-04-11T13:22:57.000+03:00
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 bc0bb9f Author: Jani Nikula <jani.nikula@intel.com> 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. Additionally this should fix the regression caused by commit fbc9fe1 Author: Aaron Lu <aaron.lu@intel.com> Date: Fri Oct 11 21:27:45 2013 +0800 ACPI / video: Do not register backlight if win8 and native interface exists which left some machines without a functioning backlight interface. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76276 Reference: https://bugzilla.kernel.org/show_bug.cgi?id=47941 Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=62281 CC: Aaron Lu <aaron.lu@intel.com> CC: Eric Griffith <EGriffith92@gmail.com> CC: Kent Baxley <kent.baxley@canonical.com> Tested-by: Kamal Mostafa <kamal@canonical.com> Tested-by: Martin <bugs@mrvanes.com> Tested-by: jrg.otte@gmail.com Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
diff --git 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);
