[PATCH 6/8] drm/i915/backlight: Add function to change brightness in nits for VESA

[Suraj Kandpal]

Create a function that fills in the value for
PANEL_TARGET_LUMINANCE_VALUE which helps in changing the luminance in
nits using VESA interface.

--v2
-Prefer using luminance over nits [Jani]

Signed-off-by: Suraj Kandpal <suraj.kand...@intel.com>
Tested-by: Ben Kao <ben....@intel.com>
Reviewed-by: Arun R Murthy <arun.r.mur...@intel.com>
---
 .../drm/i915/display/intel_dp_aux_backlight.c | 30 +++++++++++++++++++
 1 file changed, 30 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 ca5fc40fa13a..b0640b5128b1 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -474,6 +474,31 @@ static u32 intel_dp_aux_vesa_get_backlight(struct 
intel_connector *connector, en
        return connector->panel.backlight.level;
 }
 
+static int
+intel_dp_aux_vesa_set_luminance(struct intel_connector *connector, u32 level)
+{
+       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+       u8 buf[3];
+       int ret;
+
+       level = level * 1000;
+       level &= 0xffffff;
+       buf[0] = (level & 0x0000ff);
+       buf[1] = (level & 0x00ff00) >> 8;
+       buf[2] = (level & 0xff0000) >> 16;
+
+       ret = drm_dp_dpcd_write(&intel_dp->aux, 
DP_EDP_PANEL_TARGET_LUMINANCE_VALUE,
+                               buf, sizeof(buf));
+       if (ret != sizeof(buf)) {
+               drm_err(intel_dp->aux.drm_dev,
+                       "%s: Failed to set VESA Aux Luminance: %d\n",
+                       intel_dp->aux.name, ret);
+               return -EINVAL;
+       } else {
+               return 0;
+       }
+}
+
 static void
 intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, 
u32 level)
 {
@@ -481,6 +506,11 @@ intel_dp_aux_vesa_set_backlight(const struct 
drm_connector_state *conn_state, u3
        struct intel_panel *panel = &connector->panel;
        struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
+       if (panel->backlight.edp.vesa.luminance_control_support) {
+               if (!intel_dp_aux_vesa_set_luminance(connector, level))
+                       return;
+       }
+
        if (!panel->backlight.edp.vesa.info.aux_set) {
                const u32 pwm_level = intel_backlight_level_to_pwm(connector, 
level);
 
-- 
2.34.1