drm/i915: quirk no PCH_PWM_ENABLE for Dell XPS13 backlight

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=47941
BugLink: https://bugs.launchpad.net/bugs/1163720
BugLink: https://bugs.launchpad.net/bugs/1162026

Some machines suffer from non-functional backlight controls if
BLM_PCH_PWM_ENABLE is set, so provide a quirk to avoid doing so.
Apply this quirk to Dell XPS 13 models.

Tested-by: Eric Griffith <EGriffith92@gmail.com>
Tested-by: Kent Baxley <kent.baxley@canonical.com>
Cc: <stable@vger.kernel.org> # v3.8+
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -555,6 +555,7 @@ enum intel_sbi_destination {
 #define QUIRK_PIPEA_FORCE (1<<0)
 #define QUIRK_LVDS_SSC_DISABLE (1<<1)
 #define QUIRK_INVERT_BRIGHTNESS (1<<2)
+#define QUIRK_NO_PCH_PWM_ENABLE (1<<3)
 
 struct intel_fbdev;
 struct intel_fbc_work;

drivers/gpu/drm/i915/intel_display.c

@@ -9400,6 +9400,17 @@ static void quirk_invert_brightness(struct drm_device *dev)
 	DRM_INFO("applying inverted panel brightness quirk\n");
 }
 
+/*
+ * Some machines (Dell XPS13) suffer broken backlight controls if
+ * BLM_PCH_PWM_ENABLE is set.
+ */
+static void quirk_no_pcm_pwm_enable(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	dev_priv->quirks |= QUIRK_NO_PCH_PWM_ENABLE;
+	DRM_INFO("applying no-PCH_PWM_ENABLE quirk\n");
+}
+
 struct intel_quirk {
 	int device;
 	int subsystem_vendor;
@@ -9469,6 +9480,11 @@ static struct intel_quirk intel_quirks[] = {
 
 	/* Acer Aspire 4736Z */
 	{ 0x2a42, 0x1025, 0x0260, quirk_invert_brightness },
+
+	/* Dell XPS13 HD Sandy Bridge */
+	{ 0x0116, 0x1028, 0x052e, quirk_no_pcm_pwm_enable },
+	/* Dell XPS13 HD and XPS13 FHD Ivy Bridge */
+	{ 0x0166, 0x1028, 0x058b, quirk_no_pcm_pwm_enable },
 };
 
 static void intel_init_quirks(struct drm_device *dev)

drivers/gpu/drm/i915/intel_panel.c

@@ -583,7 +583,8 @@ void intel_panel_enable_backlight(struct drm_device *dev,
 		POSTING_READ(reg);
 		I915_WRITE(reg, tmp | BLM_PWM_ENABLE);
 
-		if (HAS_PCH_SPLIT(dev)) {
+		if (HAS_PCH_SPLIT(dev) &&
+		    !(dev_priv->quirks & QUIRK_NO_PCH_PWM_ENABLE)) {
 			tmp = I915_READ(BLC_PWM_PCH_CTL1);
 			tmp |= BLM_PCH_PWM_ENABLE;
 			tmp &= ~BLM_PCH_OVERRIDE_ENABLE;