[Intel-gfx] [PATCH v2 3/4] 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.

Change-Id: I7140d4e838c654b6527df38b5780ad1533848d6c
Signed-off-by: Puthikorn Voravootivat <put...@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 532176f1108a..420a5aada652 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)
+{
+       u8 dbc[] = { DIV_ROUND_CLOSEST(min, 5), DIV_ROUND_CLOSEST(max, 5) };
+       drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET,
+                         dbc, sizeof(dbc));
+}
+
 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);
@@ -110,16 +124,15 @@ 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;
-               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 when it is already DPCD mode */
@@ -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

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