[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 <ams...@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