drm/vc4: hdmi: Add a workqueue to set scrambling

It looks like some displays (like the LG 27UL850-W) don't enable the
scrambling when the HDMI driver enables it. However, if we set later the
scrambler enable bit, the display will work as expected.

Let's create delayed work queue to periodically look at the display
scrambling status, and if it's not set yet try to enable it again.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210507150515.257424-12-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -538,6 +538,8 @@ static bool vc4_hdmi_supports_scrambling(struct drm_encoder *encoder,
 	return true;
 }
 
+#define SCRAMBLING_POLLING_DELAY_MS	1000
+
 static void vc4_hdmi_enable_scrambling(struct drm_encoder *encoder)
 {
 	struct drm_display_mode *mode = &encoder->crtc->state->adjusted_mode;
@@ -554,6 +556,9 @@ static void vc4_hdmi_enable_scrambling(struct drm_encoder *encoder)
 
 	HDMI_WRITE(HDMI_SCRAMBLER_CTL, HDMI_READ(HDMI_SCRAMBLER_CTL) |
 		   VC5_HDMI_SCRAMBLER_CTL_ENABLE);
+
+	queue_delayed_work(system_wq, &vc4_hdmi->scrambling_work,
+			   msecs_to_jiffies(SCRAMBLING_POLLING_DELAY_MS));
 }
 
 static void vc4_hdmi_disable_scrambling(struct drm_encoder *encoder)
@@ -572,6 +577,9 @@ static void vc4_hdmi_disable_scrambling(struct drm_encoder *encoder)
 	if (crtc && !vc4_hdmi_mode_needs_scrambling(&crtc->mode))
 		return;
 
+	if (delayed_work_pending(&vc4_hdmi->scrambling_work))
+		cancel_delayed_work_sync(&vc4_hdmi->scrambling_work);
+
 	HDMI_WRITE(HDMI_SCRAMBLER_CTL, HDMI_READ(HDMI_SCRAMBLER_CTL) &
 		   ~VC5_HDMI_SCRAMBLER_CTL_ENABLE);
 
@@ -579,6 +587,22 @@ static void vc4_hdmi_disable_scrambling(struct drm_encoder *encoder)
 	drm_scdc_set_high_tmds_clock_ratio(vc4_hdmi->ddc, false);
 }
 
+static void vc4_hdmi_scrambling_wq(struct work_struct *work)
+{
+	struct vc4_hdmi *vc4_hdmi = container_of(to_delayed_work(work),
+						 struct vc4_hdmi,
+						 scrambling_work);
+
+	if (drm_scdc_get_scrambling_status(vc4_hdmi->ddc))
+		return;
+
+	drm_scdc_set_high_tmds_clock_ratio(vc4_hdmi->ddc, true);
+	drm_scdc_set_scrambling(vc4_hdmi->ddc, true);
+
+	queue_delayed_work(system_wq, &vc4_hdmi->scrambling_work,
+			   msecs_to_jiffies(SCRAMBLING_POLLING_DELAY_MS));
+}
+
 static void vc4_hdmi_encoder_post_crtc_disable(struct drm_encoder *encoder,
 					       struct drm_atomic_state *state)
 {
@@ -2087,6 +2111,7 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
 	vc4_hdmi = devm_kzalloc(dev, sizeof(*vc4_hdmi), GFP_KERNEL);
 	if (!vc4_hdmi)
 		return -ENOMEM;
+	INIT_DELAYED_WORK(&vc4_hdmi->scrambling_work, vc4_hdmi_scrambling_wq);
 
 	dev_set_drvdata(dev, vc4_hdmi);
 	encoder = &vc4_hdmi->encoder.base.base;

drivers/gpu/drm/vc4/vc4_hdmi.h

@@ -129,6 +129,8 @@ struct vc4_hdmi {
 	struct vc4_hdmi_encoder encoder;
 	struct drm_connector connector;
 
+	struct delayed_work scrambling_work;
+
 	struct i2c_adapter *ddc;
 	void __iomem *hdmicore_regs;
 	void __iomem *hd_regs;