[Intel-gfx] [PATCH 3/5] drm/i915: Support dynamic backlight via DPCD register

[Puthikorn Voravootivat]

This patch enables dynamic backlight by default 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 at chromium.org>
---
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 31 +++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index 16cd1265d264..643b604be2de 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -97,10 +97,24 @@ intel_dp_aux_set_backlight(struct intel_connector *connector, u32 level)
 	}
 }
 
+/*
+ * Set minimum / maximum dynamic brightness percentage. This value is expressed
+ * as the percentage of normal brightness in 5% increments.
+ */
+static void intel_dp_aux_set_dynamic_backlight_percent(
+		struct intel_dp *intel_dp, u32 min, u32 max)
+{
+	drm_dp_dpcd_writeb(&intel_dp->aux,
+		DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET, min / 5);
+	drm_dp_dpcd_writeb(&intel_dp->aux,
+		DP_EDP_DBC_MAXIMUM_BRIGHTNESS_SET, max / 5);
+}
+
 static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
 	uint8_t dpcd_buf = 0;
+	uint8_t new_dpcd_buf = 0;
 	uint8_t edp_backlight_mode = 0;
 
 	set_aux_backlight_enable(intel_dp, true);
@@ -110,15 +124,14 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 		return;
 	}
 
+	new_dpcd_buf = dpcd_buf;
 	edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
 
 	switch (edp_backlight_mode) {
 	case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
 	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
-		dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
-		dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
-		drm_dp_dpcd_writeb(&intel_dp->aux,
-			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, dpcd_buf);
+		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
+		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
 		break;
 
 	/* Do nothing in these cases */
@@ -127,6 +140,16 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 	default:
 		break;
 	}
+
+	if (intel_dp->edp_dpcd[2] & DP_EDP_DYNAMIC_BACKLIGHT_CAP) {
+		new_dpcd_buf |= DP_EDP_DYNAMIC_BACKLIGHT_ENABLE;
+		intel_dp_aux_set_dynamic_backlight_percent(intel_dp, 0, 100);
+	}
+
+	if (new_dpcd_buf != dpcd_buf) {
+		drm_dp_dpcd_writeb(&intel_dp->aux,
+			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
+	}
 }
 
 static void intel_dp_aux_disable_backlight(struct intel_connector *connector)
-- 
2.12.0.246.ga2ecc84866-goog