[Intel-gfx] [PATCH v4 1/6] drm/i915: Add DPCD preferred mode for backlight control

[Puthikorn Voravootivat]

Currently the intel_dp_aux_backlight driver requires eDP panel
to not also support backlight adjustment via PWM pin to use
this driver.

This force the eDP panel that support both ways of backlight
adjustment to do it via PWM pin.

This patch adds the new prefer DPCD mode in the i915_param
to make it enable to prefer DPCD over the PWM via kernel param.

This patch also add a check to DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
in set_aux_backlight_enable() since the backlight enablement
can be done via BL_ENABLE eDP connector pin in the case that
it does not support doing that via AUX.

Cc: Jani Nikula <jani.nikula at linux.intel.com>
Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
---
 drivers/gpu/drm/i915/i915_params.c            |  6 ++---
 drivers/gpu/drm/i915/i915_params.h            |  2 +-
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 33 +++++++++++++++++++--------
 3 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index b6a7e363d076..960393dd5edf 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 = 0,
 	.enable_gvt = false,
 };
 
@@ -246,9 +246,9 @@ 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(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 (0:disable (default), 1:prefer PWM pin, 2: prefer DPCD)");
 
 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..bf6e2c60f697 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -51,6 +51,7 @@
 	func(int, use_mmio_flip); \
 	func(int, mmio_debug); \
 	func(int, edp_vswing); \
+	func(int, enable_dpcd_backlight); \
 	func(unsigned int, inject_load_failure); \
 	/* leave bools at the end to not create holes */ \
 	func(bool, alpha_support); \
@@ -66,7 +67,6 @@
 	func(bool, verbose_state_checks); \
 	func(bool, nuclear_pageflip); \
 	func(bool, enable_dp_mst); \
-	func(bool, 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 6532e226db29..42f73d9a3ccf 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -28,6 +28,10 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
 {
 	uint8_t reg_val = 0;
 
+	/* Early return when display use other mechanism to enable backlight. */
+	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
+		return;
+
 	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
 			      &reg_val) < 0) {
 		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
@@ -138,27 +142,36 @@ static bool
 intel_dp_aux_display_control_capable(struct intel_connector *connector)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
+	bool supported;
 
 	/* 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[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
-	    !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) ||
-	      (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))) {
-		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
-		return true;
+	switch (i915.enable_dpcd_backlight) {
+	case 1: /* prefer PWM pin */
+		supported = (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
+			    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
+			    !(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) &&
+			    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP);
+		break;
+	case 2: /* prefer DPCD */
+		supported = (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
+			    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
+		break;
+	default:
+		supported = false;
 	}
-	return false;
+
+	if (supported)
+		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
+
+	return supported;
 }
 
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 {
 	struct intel_panel *panel = &intel_connector->panel;
 
-	if (!i915.enable_dpcd_backlight)
-		return -ENODEV;
-
 	if (!intel_dp_aux_display_control_capable(intel_connector))
 		return -ENODEV;
 
-- 
2.12.1.500.gab5fba24ee-goog