[PATCH 4/7] drm/i915/backlight: Modify function to get VESA brightness in Nits

[Suraj Kandpal]

Modify vesa_get_brightness function to take into account
luminance_control_support and based on that read the appropriate
register and return the value.

--v2
-Changes since we now use luminance instead of nits

Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
Tested-by: Ben Kao <ben.kao at intel.com>
---
 .../drm/i915/display/intel_dp_aux_backlight.c | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 84126e7d1716..a733b5623563 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -451,6 +451,26 @@ intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pi
 /* VESA backlight callbacks */
 static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
 {
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	struct intel_panel *panel = &connector->panel;
+	u8 buf[3];
+	u32 val = 0;
+	int ret;
+
+	if (panel->backlight.edp.vesa.luminance_control_support) {
+		ret = drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf,
+				       sizeof(buf));
+		if (ret < 0) {
+			drm_err(intel_dp->aux.drm_dev,
+				"[CONNECTOR:%d:%s] Failed to read Luminance from DPCD\n",
+				connector->base.base.id, connector->base.name);
+			return 0;
+		}
+
+		val |= buf[0] | buf[1] << 8 | buf[2] << 16;
+		return val / 1000;
+	}
+
 	return connector->panel.backlight.level;
 }
 
-- 
2.34.1