drm/i915: don't warn if backlight unexpectedly enabled

commit 813008cd upstream.

BIOS or firmware can modify hardware state during suspend/resume,
for example on the Toshiba CB35 or Lenovo T400, so log a debug message
instead of a warning if the backlight is unexpectedly enabled.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80930
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/gpu/drm/i915/intel_panel.c

@@ -711,7 +711,7 @@ static void pch_enable_backlight(struct intel_connector *connector)
 
 	cpu_ctl2 = I915_READ(BLC_PWM_CPU_CTL2);
 	if (cpu_ctl2 & BLM_PWM_ENABLE) {
-		WARN(1, "cpu backlight already enabled\n");
+		DRM_DEBUG_KMS("cpu backlight already enabled\n");
 		cpu_ctl2 &= ~BLM_PWM_ENABLE;
 		I915_WRITE(BLC_PWM_CPU_CTL2, cpu_ctl2);
 	}
@@ -755,7 +755,7 @@ static void i9xx_enable_backlight(struct intel_connector *connector)
 
 	ctl = I915_READ(BLC_PWM_CTL);
 	if (ctl & BACKLIGHT_DUTY_CYCLE_MASK_PNV) {
-		WARN(1, "backlight already enabled\n");
+		DRM_DEBUG_KMS("backlight already enabled\n");
 		I915_WRITE(BLC_PWM_CTL, 0);
 	}
 
@@ -786,7 +786,7 @@ static void i965_enable_backlight(struct intel_connector *connector)
 
 	ctl2 = I915_READ(BLC_PWM_CTL2);
 	if (ctl2 & BLM_PWM_ENABLE) {
-		WARN(1, "backlight already enabled\n");
+		DRM_DEBUG_KMS("backlight already enabled\n");
 		ctl2 &= ~BLM_PWM_ENABLE;
 		I915_WRITE(BLC_PWM_CTL2, ctl2);
 	}
@@ -820,7 +820,7 @@ static void vlv_enable_backlight(struct intel_connector *connector)
 
 	ctl2 = I915_READ(VLV_BLC_PWM_CTL2(pipe));
 	if (ctl2 & BLM_PWM_ENABLE) {
-		WARN(1, "backlight already enabled\n");
+		DRM_DEBUG_KMS("backlight already enabled\n");
 		ctl2 &= ~BLM_PWM_ENABLE;
 		I915_WRITE(VLV_BLC_PWM_CTL2(pipe), ctl2);
 	}