drm/i915: panel: invert brightness via quirk

A machine may need to invert the panel backlight brightness value. This
patch adds the infrastructure for a quirk to do so.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/kernel-parameters.txt

@@ -967,14 +967,19 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	i8k.restricted	[HW] Allow controlling fans only if SYS_ADMIN
 			capability is set.
 
-	i915.invert_brightness
+	i915.invert_brightness=
 			[DRM] Invert the sense of the variable that is used to
 			set the brightness of the panel backlight. Normally a
-			value of 0 indicates backlight switched off, and the
-			maximum value sets the backlight to maximum brightness.
-			If this parameter is specified, a value of 0 sets the
-			backlight to maximum brightness, and the maximum value
-			switches the backlight off.
+			brightness value of 0 indicates backlight switched off,
+			and the maximum of the brightness value sets the backlight
+			to maximum brightness. If this parameter is set to 0
+			(default) and the machine requires it, or this parameter
+			is set to 1, a brightness value of 0 sets the backlight
+			to maximum brightness, and the maximum of the brightness
+			value switches the backlight off.
+			-1 -- never invert brightness
+			 0 -- machine default
+			 1 -- force brightness inversion
 
 	icn=		[HW,ISDN]
 			Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]

drivers/gpu/drm/i915/i915_drv.h

@@ -295,6 +295,7 @@ enum intel_pch {
 
 #define QUIRK_PIPEA_FORCE (1<<0)
 #define QUIRK_LVDS_SSC_DISABLE (1<<1)
+#define QUIRK_INVERT_BRIGHTNESS (1<<2)
 
 struct intel_fbdev;
 struct intel_fbc_work;

drivers/gpu/drm/i915/intel_display.c

@@ -9020,6 +9020,15 @@ static void quirk_ssc_force_disable(struct drm_device *dev)
 	dev_priv->quirks |= QUIRK_LVDS_SSC_DISABLE;
 }
 
+/*
+ * A machine may need to invert the panel backlight brightness value
+ */
+static void quirk_invert_brightness(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	dev_priv->quirks |= QUIRK_INVERT_BRIGHTNESS;
+}
+
 struct intel_quirk {
 	int device;
 	int subsystem_vendor;

drivers/gpu/drm/i915/intel_panel.c

@@ -192,15 +192,22 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)
 	return max;
 }
 
-static bool i915_panel_invert_brightness;
-MODULE_PARM_DESC(invert_brightness, "Invert backlight brightness, please "
+static int i915_panel_invert_brightness;
+MODULE_PARM_DESC(invert_brightness, "Invert backlight brightness "
+	"(-1 force normal, 0 machine defaults, 1 force inversion), please "
 	"report PCI device ID, subsystem vendor and subsystem device ID "
 	"to dri-devel@lists.freedesktop.org, if your machine needs it. "
 	"It will then be included in an upcoming module version.");
-module_param_named(invert_brightness, i915_panel_invert_brightness, bool, 0600);
+module_param_named(invert_brightness, i915_panel_invert_brightness, int, 0600);
 static u32 intel_panel_compute_brightness(struct drm_device *dev, u32 val)
 {
-	if (i915_panel_invert_brightness)
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (i915_panel_invert_brightness < 0)
+		return val;
+
+	if (i915_panel_invert_brightness > 0 ||
+	    dev_priv->quirks & QUIRK_INVERT_BRIGHTNESS)
 		return intel_panel_get_max_backlight(dev) - val;
 
 	return val;