drm/i915: Add option to support dynamic backlight via DPCD

This patch adds option to enable dynamic backlight for eDP
panel that supports this feature via DPCD register and
set minimum / maximum brightness to 0% and 100% of the
normal brightness.
Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170622190339.142671-4-puthik@chromium.org

drivers/gpu/drm/i915/i915_params.c

@@ -65,6 +65,7 @@ struct i915_params i915 __read_mostly = {
 	.inject_load_failure = 0,
 	.enable_dpcd_backlight = -1,
 	.enable_gvt = false,
+	.enable_dbc = true,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -254,3 +255,7 @@ MODULE_PARM_DESC(enable_dpcd_backlight,
 module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
 MODULE_PARM_DESC(enable_gvt,
 	"Enable support for Intel GVT-g graphics virtualization host support(default:false)");
+
+module_param_named_unsafe(enable_dbc, i915.enable_dbc, bool, 0600);
+MODULE_PARM_DESC(enable_dbc,
+	"Enable support for dynamic backlight control (default:true)");

drivers/gpu/drm/i915/i915_params.h

@@ -67,7 +67,8 @@
 	func(bool, verbose_state_checks); \
 	func(bool, nuclear_pageflip); \
 	func(bool, enable_dp_mst); \
-	func(bool, enable_gvt)
+	func(bool, enable_gvt); \
+	func(bool, enable_dbc)
 
 #define MEMBER(T, member) T member
 struct i915_params {

drivers/gpu/drm/i915/intel_dp_aux_backlight.c

@@ -173,6 +173,24 @@ static bool intel_dp_aux_set_pwm_freq(struct intel_connector *connector)
 	return true;
 }
 
+/*
+* Set minimum / maximum dynamic brightness percentage. This value is expressed
+* as the percentage of normal brightness in 5% increments.
+*/
+static bool
+intel_dp_aux_set_dynamic_backlight_percent(struct intel_dp *intel_dp,
+					   u32 min, u32 max)
+{
+	u8 dbc[] = { DIV_ROUND_CLOSEST(min, 5), DIV_ROUND_CLOSEST(max, 5) };
+
+	if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET,
+			  dbc, sizeof(dbc)) < 0) {
+		DRM_DEBUG_KMS("Failed to write aux DBC brightness level\n");
+		return false;
+	}
+	return true;
+}
+
 static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_state,
 					  const struct drm_connector_state *conn_state)
 {
@@ -208,6 +226,14 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st
 		if (intel_dp_aux_set_pwm_freq(connector))
 			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
 
+	if (i915.enable_dbc &&
+	    (intel_dp->edp_dpcd[2] & DP_EDP_DYNAMIC_BACKLIGHT_CAP)) {
+		if(intel_dp_aux_set_dynamic_backlight_percent(intel_dp, 0, 100)) {
+			new_dpcd_buf |= DP_EDP_DYNAMIC_BACKLIGHT_ENABLE;
+			DRM_DEBUG_KMS("Enable dynamic brightness.\n");
+		}
+	}
+
 	if (new_dpcd_buf != dpcd_buf) {
 		if (drm_dp_dpcd_writeb(&intel_dp->aux,
 			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {