[PATCH v9 3/5] drm/i915: Add option to support dynamic backlight via DPCD

[Puthikorn Voravootivat]

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 at chromium.org>
---
 drivers/gpu/drm/i915/i915_params.c            |  5 ++++
 drivers/gpu/drm/i915/i915_params.h            |  3 +-
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 42 ++++++++++++++++++++++-----
 3 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 13cf3f1572ab..6eaf660e74da 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/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 = false,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -255,3 +256,7 @@ 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(enable_dbc, i915.enable_dbc, bool, 0600);
+MODULE_PARM_DESC(enable_dbc,
+	"Enable support for dynamic backlight control (default:false)");
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index ac02efce6e22..2de3e2850b54 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -67,7 +67,8 @@
 	func(bool, nuclear_pageflip); \
 	func(bool, enable_dp_mst); \
 	func(int, enable_dpcd_backlight); \
-	func(bool, enable_gvt)
+	func(bool, enable_gvt); \
+	func(bool, enable_dbc)
 
 #define MEMBER(T, member) T member
 struct i915_params {
diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index 16ba1924308d..f1b7855a2d2a 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -100,11 +100,26 @@ 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)
+{
+	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");
+	}
+}
+
 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 edp_backlight_mode = 0;
+	uint8_t dpcd_buf, new_dpcd_buf, edp_backlight_mode;
 
 	if (drm_dp_dpcd_readb(&intel_dp->aux,
 			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
@@ -113,18 +128,15 @@ 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:
 	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
-		dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
-		dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
-		if (drm_dp_dpcd_writeb(&intel_dp->aux,
-			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, dpcd_buf) < 0) {
-			DRM_DEBUG_KMS("Failed to write aux backlight mode\n");
-		}
+		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
+		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
 		break;
 
 	/* Do nothing when it is already DPCD mode */
@@ -133,6 +145,20 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 		break;
 	}
 
+	if (i915.enable_dbc &&
+	    (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);
+		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) {
+			DRM_DEBUG_KMS("Failed to write aux backlight mode\n");
+		}
+	}
+
 	set_aux_backlight_enable(intel_dp, true);
 	intel_dp_aux_set_backlight(connector, connector->panel.backlight.level);
 }
-- 
2.13.0.219.gdb65acc882-goog