[PATCH 2/2] drm/bridge: analogix: Enable EDP_BACKLIGHT_FREQ_PWM_PIN_PASSTHRU

[Alexandru M Stan]

Configure the DPCD registers for the backlight to respect the pwm frequency
of the input. We sometimes don't want it to generate its own.

Signed-off-by: Alexandru M Stan <amstan at chromium.org>
---

 drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 48 ++++++++++++++++++++++
 drivers/gpu/drm/bridge/analogix/analogix_dp_core.h |  1 +
 2 files changed, 49 insertions(+)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index 5c52307146c7..b830403be8eb 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -916,6 +916,46 @@ static irqreturn_t analogix_dp_irq_thread(int irq, void *arg)
 	return IRQ_HANDLED;
 }
 
+static int analogix_dp_backlight_pwm_passthru(struct analogix_dp_device *dp)
+{
+	u8 value;
+	const u8 expected_cap = DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP |
+				DP_EDP_BACKLIGHT_FREQ_PWM_PIN_PASSTHRU_CAP;
+	int ret = 0;
+
+	ret = drm_dp_dpcd_readb(&dp->aux, DP_EDP_BACKLIGHT_ADJUSTMENT_CAP,
+				&value);
+	if (ret != 1) {
+		DRM_DEV_ERROR(dp->dev,
+			"backlight PWM passthru: Can't read BACKLIGHT_ADJUSTMENT_CAP\n");
+		return ret;
+	}
+
+	if ((value & expected_cap) != expected_cap) {
+		DRM_DEV_ERROR(dp->dev,
+			"panel doesn't support backlight PWM passthru, BACKLIGHT_ADJUSTMENT_CAP=0x%02x\n",
+			value);
+		return -1;
+	}
+
+	ret = drm_dp_dpcd_readb(&dp->aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
+				&value);
+	if (ret != 1) {
+		DRM_DEV_ERROR(dp->dev,
+			"backlight PWM passthru: Can't read BACKLIGHT_MODE_SET_REGISTER\n");
+		return ret;
+	}
+
+	value |= DP_EDP_BACKLIGHT_FREQ_PWM_PIN_PASSTHRU_ENABLE;
+	ret = drm_dp_dpcd_writeb(&dp->aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
+				 value);
+	if (ret != 1) {
+		DRM_DEV_ERROR(dp->dev,
+			"backlight PWM passthru: Can't write BACKLIGHT_MODE_SET_REGISTER\n");
+	}
+	return ret;
+}
+
 static void analogix_dp_commit(struct analogix_dp_device *dp)
 {
 	int ret;
@@ -954,6 +994,12 @@ static void analogix_dp_commit(struct analogix_dp_device *dp)
 	dp->psr_enable = analogix_dp_detect_sink_psr(dp);
 	if (dp->psr_enable)
 		analogix_dp_enable_sink_psr(dp);
+
+	if (dp->backlight_pwm_passthru) {
+		if (analogix_dp_backlight_pwm_passthru(dp) != 1)
+			DRM_DEV_ERROR(dp->dev,
+				 "Could not enable backlight pwm pin passthru.\n");
+	}
 }
 
 /*
@@ -1424,6 +1470,8 @@ analogix_dp_bind(struct device *dev, struct drm_device *drm_dev,
 	if (IS_ERR(dp->reg_base))
 		return ERR_CAST(dp->reg_base);
 
+	dp->backlight_pwm_passthru =
+	       of_property_read_bool(dev->of_node, "backlight-pwm-passthru");
 	dp->force_hpd = of_property_read_bool(dev->of_node, "force-hpd");
 
 	dp->hpd_gpio = of_get_named_gpio(dev->of_node, "hpd-gpios", 0);
diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
index 6a96ef7e6934..aea51413e78e 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.h
@@ -171,6 +171,7 @@ struct analogix_dp_device {
 	struct phy		*phy;
 	int			dpms_mode;
 	int			hpd_gpio;
+	bool			backlight_pwm_passthru;
 	bool                    force_hpd;
 	bool			psr_enable;
 	bool			fast_train_support;
-- 
2.13.5