drm/i915: Parse LFP brightness control field in VBT

These fields in VBT indicates the PWM source which
is used and also the controller number.

v2 by Jani: check for out of bounds access, some renames, change default
type, etc.

v3 by Jani: s/INTEL_BACKLIGHT_CABC/INTEL_BACKLIGHT_DSI_DCS/
Signed-off-by: Deepak M <m.deepak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/eee2f7b683a081f006a7df1ddad9b20fbf53c48c.1461676337.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1492,6 +1492,7 @@ struct intel_vbt_data {
 		bool present;
 		bool active_low_pwm;
 		u8 min_brightness;	/* min_brightness/255 of max */
+		enum intel_backlight_type type;
 	} backlight;
 
 	/* MIPI DSI */

drivers/gpu/drm/i915/intel_bios.c

@@ -318,6 +318,15 @@ parse_lfp_backlight(struct drm_i915_private *dev_priv,
 		return;
 	}
 
+	dev_priv->vbt.backlight.type = INTEL_BACKLIGHT_DISPLAY_DDI;
+	if (bdb->version >= 191 &&
+	    get_blocksize(backlight_data) >= sizeof(*backlight_data)) {
+		const struct bdb_lfp_backlight_control_method *method;
+
+		method = &backlight_data->backlight_control[panel_type];
+		dev_priv->vbt.backlight.type = method->type;
+	}
+
 	dev_priv->vbt.backlight.pwm_freq_hz = entry->pwm_freq_hz;
 	dev_priv->vbt.backlight.active_low_pwm = entry->active_low_pwm;
 	dev_priv->vbt.backlight.min_brightness = entry->min_brightness;

drivers/gpu/drm/i915/intel_bios.h

@@ -30,6 +30,14 @@
 #ifndef _INTEL_BIOS_H_
 #define _INTEL_BIOS_H_
 
+enum intel_backlight_type {
+	INTEL_BACKLIGHT_PMIC,
+	INTEL_BACKLIGHT_LPSS,
+	INTEL_BACKLIGHT_DISPLAY_DDI,
+	INTEL_BACKLIGHT_DSI_DCS,
+	INTEL_BACKLIGHT_PANEL_DRIVER_INTERFACE,
+};
+
 struct edp_power_seq {
 	u16 t1_t3;
 	u16 t8;

drivers/gpu/drm/i915/intel_vbt_defs.h

@@ -446,10 +446,16 @@ struct bdb_lfp_backlight_data_entry {
 	u8 obsolete3;
 } __packed;
 
+struct bdb_lfp_backlight_control_method {
+	u8 type:4;
+	u8 controller:4;
+} __packed;
+
 struct bdb_lfp_backlight_data {
 	u8 entry_size;
 	struct bdb_lfp_backlight_data_entry data[16];
 	u8 level[16];
+	struct bdb_lfp_backlight_control_method backlight_control[16];
 } __packed;
 
 struct aimdb_header {