[Intel-gfx] [PATCH 3/3] drm/i915: Add backlight Control using DPCD registers for DP connectors

[Yetunde Adebisi]

This patch enables support for DPCD backlight control for DP connectors.
The VESA spec defines DPCD backlight control only for eDP but some add-on
cards like the Chrontel CH7511B DP-LVDS cards have the display control
DPCD registers enabled.
This patch registers a backlight device exposed via sysfs that controls the
connected panel backlight by writing to DPCD registers on the CH7511B
add-on card

Signed-off-by: Yetunde Adebisi <yetundex.adebisi at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c               | 25 ++++++++++++++++++++
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c |  7 ++++++
 drivers/gpu/drm/i915/intel_drv.h              |  2 ++
 drivers/gpu/drm/i915/intel_panel.c            | 33 +++++++++++++++++++--------
 4 files changed, 57 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 9ccc581..bf79ef4 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -5718,6 +5718,30 @@ intel_dp_drrs_init(struct intel_connector *intel_connector,
 	return downclock_mode;
 }
 
+/*
+ * Called on DP connector initialization to check for aux backlight control
+ * capability on the sink device and if present, initialize it.
+ */
+static void intel_dp_init_aux_backlight(struct intel_dp *intel_dp,
+		struct drm_connector *connector)
+{
+	struct intel_connector *intel_connector = to_intel_connector(connector);
+
+	if (is_edp(intel_dp))
+		return;
+
+	if (i915.enable_dpcd_backlight &&
+			(intel_dp_dpcd_read_wake(&intel_dp->aux, DP_EDP_DPCD_REV,
+					intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd)) ==
+							sizeof(intel_dp->edp_dpcd)) &&
+							intel_dp_aux_init_backlight_funcs(intel_connector) == 0) {
+		intel_panel_setup_backlight(connector, INVALID_PIPE);
+
+		intel_connector->panel.backlight.power = intel_dp_aux_backlight_power;
+		intel_connector->panel.backlight.enabled = true;
+		}
+}
+
 static bool intel_edp_init_connector(struct intel_dp *intel_dp,
 				     struct intel_connector *intel_connector)
 {
@@ -5955,6 +5979,7 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
 		goto fail;
 	}
 
+	intel_dp_init_aux_backlight(intel_dp, connector);
 	intel_dp_add_properties(intel_dp, connector);
 
 	/* For G4X desktop chip, PEG_BAND_GAP_DATA 3:0 must first be written
diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index a5361d6..efa657f 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -168,3 +168,10 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 
 	return 0;
 }
+
+void intel_dp_aux_backlight_power(struct intel_connector *connector,
+				      bool enable)
+{
+	set_aux_backlight_enable(enc_to_intel_dp(&connector->encoder->base),
+			enable);
+}
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 6dd24c4..1b03c77 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1342,6 +1342,8 @@ ssize_t intel_dp_dpcd_read_wake(struct drm_dp_aux *aux, unsigned int offset,
 
 /* intel_dp_aux_backlight.c */
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector);
+void intel_dp_aux_backlight_power(struct intel_connector *connector,
+				      bool enable);
 
 /* intel_dp_mst.c */
 int intel_dp_mst_encoder_init(struct intel_digital_port *intel_dig_port, int conn_id);
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 68fb3bd..5074457 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1193,16 +1193,29 @@ static int intel_backlight_device_register(struct intel_connector *connector)
 	else
 		props.power = FB_BLANK_POWERDOWN;
 
-	/*
-	 * Note: using the same name independent of the connector prevents
-	 * registration of multiple backlight devices in the driver.
-	 */
-	panel->backlight.device =
-		backlight_device_register("intel_backlight",
-					  connector->base.kdev,
-					  connector,
-					  &intel_backlight_device_ops, &props);
-
+	if (connector->base.connector_type == DRM_MODE_CONNECTOR_DisplayPort) {
+		char *name = kasprintf(GFP_KERNEL, "intel_aux_backlight-%s",
+				connector->base.name);
+		if (!name)
+			return -ENOMEM;
+
+		panel->backlight.device =
+			backlight_device_register(name,
+						  connector->base.kdev,
+						  connector,
+						  &intel_backlight_device_ops, &props);
+			kfree(name);
+	} else {
+		/*
+		 * Note: using the same name independent of the connector prevents
+		 * registration of multiple backlight devices in the driver.
+		 */
+		panel->backlight.device =
+			backlight_device_register("intel_backlight",
+						  connector->base.kdev,
+						  connector,
+						  &intel_backlight_device_ops, &props);
+	}
 	if (IS_ERR(panel->backlight.device)) {
 		DRM_ERROR("Failed to register backlight: %ld\n",
 			  PTR_ERR(panel->backlight.device));
-- 
1.9.3