[PATCH v10 1/3] drm/i915: Add heuristic to determine better way to adjust brightness

[Puthikorn Voravootivat <puthik@chromium.org>]

Add heuristic to decide that AUX or PWM pin should use for
backlight brightness adjustment and modify i915 param description
to have auto, force disable, and force enable.

The heuristic to determine that using AUX pin is better than using
PWM pin is that the panel support any of the feature list here.
- Regional backlight brightness adjustment
- Backlight PWM frequency set
- More than 8 bits resolution of brightness level
- Backlight enablement via AUX and not by BL_ENABLE pin

Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
---
 drivers/gpu/drm/i915/i915_params.c            |  7 +--
 drivers/gpu/drm/i915/i915_params.h            |  2 +-
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 64 +++++++++++++++++++++++++--
 3 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index b6a7e363d076..3758ae1f11b4 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -63,7 +63,7 @@ struct i915_params i915 __read_mostly = {
 	.huc_firmware_path = NULL,
 	.enable_dp_mst = true,
 	.inject_load_failure = 0,
-	.enable_dpcd_backlight = false,
+	.enable_dpcd_backlight = -1,
 	.enable_gvt = false,
 };
 
@@ -246,9 +246,10 @@ MODULE_PARM_DESC(enable_dp_mst,
 module_param_named_unsafe(inject_load_failure, i915.inject_load_failure, uint, 0400);
 MODULE_PARM_DESC(inject_load_failure,
 	"Force an error after a number of failure check points (0:disabled (default), N:force failure at the Nth failure check point)");
-module_param_named(enable_dpcd_backlight, i915.enable_dpcd_backlight, bool, 0600);
+module_param_named_unsafe(enable_dpcd_backlight, i915.enable_dpcd_backlight, int, 0600);
 MODULE_PARM_DESC(enable_dpcd_backlight,
-	"Enable support for DPCD backlight control (default:false)");
+	"Enable support for DPCD backlight control "
+	"(-1:auto (default), 0:force disable, 1:force enabled if supported");
 
 module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
 MODULE_PARM_DESC(enable_gvt,
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index 34148cc8637c..ac02efce6e22 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -66,7 +66,7 @@
 	func(bool, verbose_state_checks); \
 	func(bool, nuclear_pageflip); \
 	func(bool, enable_dp_mst); \
-	func(bool, enable_dpcd_backlight); \
+	func(int, enable_dpcd_backlight); \
 	func(bool, enable_gvt)
 
 #define MEMBER(T, member) T member
diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index a0995c00fc84..c89aae804659 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -43,6 +43,9 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
 	else
 		reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
 
+	/* TODO: If the panel also support enabling backlight via BL_ENABLE pin,
+	 * the backlight will be enabled again in _intel_edp_backlight_on()
+	 */
 	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
 			       reg_val) != 1) {
 		DRM_DEBUG_KMS("Failed to %s aux backlight\n",
@@ -168,15 +171,66 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
 	/* Check the  eDP Display control capabilities registers to determine if
 	 * the panel can support backlight control over the aux channel
 	 */
-	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
-	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
-	    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
+	if ((intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
+	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
 		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
 		return true;
 	}
 	return false;
 }
 
+/*
+ * Heuristic function whether we should use AUX for backlight adjustment or not.
+ *
+ * We should use AUX for backlight brightness adjustment if panel doesn't this
+ * via PWM pin or using AUX is better than using PWM pin.
+ *
+ * The heuristic to determine that using AUX pin is better than using PWM pin is
+ * that the panel support any of the feature list here.
+ * - Regional backlight brightness adjustment
+ * - Backlight PWM frequency set
+ * - More than 8 bits resolution of brightness level
+ * - Backlight enablement via AUX and not by BL_ENABLE pin
+ *
+ * If all above are not true, assume that using PWM pin is better.
+ */
+static bool
+intel_dp_aux_display_control_heuristic(struct intel_connector *connector)
+{
+	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
+	uint8_t reg_val;
+
+	/* Panel doesn't support adjusting backlight brightness via PWN pin */
+	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
+		return true;
+
+	/* Panel supports regional backlight brightness adjustment */
+	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_GENERAL_CAP_3,
+			      &reg_val) != 1) {
+		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
+			       DP_EDP_GENERAL_CAP_3);
+		return false;
+	}
+	if (reg_val > 0)
+		return true;
+
+	/* Panel supports backlight PWM frequency set */
+	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
+		return true;
+
+	/* Panel supports more than 8 bits resolution of brightness level */
+	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
+		return true;
+
+	/* Panel supports enabling backlight via AUX but not by BL_ENABLE pin */
+	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
+	    !(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP))
+		return true;
+
+	return false;
+
+}
+
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 {
 	struct intel_panel *panel = &intel_connector->panel;
@@ -187,6 +241,10 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 	if (!intel_dp_aux_display_control_capable(intel_connector))
 		return -ENODEV;
 
+	if (i915.enable_dpcd_backlight == -1 &&
+	    !intel_dp_aux_display_control_heuristic(intel_connector))
+		return -ENODEV;
+
 	panel->backlight.setup = intel_dp_aux_setup_backlight;
 	panel->backlight.enable = intel_dp_aux_enable_backlight;
 	panel->backlight.disable = intel_dp_aux_disable_backlight;
-- 
2.13.0.219.gdb65acc882-goog

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