drm/bridge/lontium-lt9611uxc: move HPD notification out of IRQ handler

drm hotplug handling code (drm_client_dev_hotplug()) can wait on mutex,
thus delaying further lt9611uxc IRQ events processing.  It was observed
occasionally during bootups, when drm_client_modeset_probe() was waiting
for EDID ready event, which was delayed because IRQ handler was stuck
trying to deliver hotplug event.
Move hotplug notifications from IRQ handler to separate work to be able
to process IRQ events without delays.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Fixes: 0cbbd5b1a0 ("drm: bridge: add support for lontium LT9611UXC bridge")
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121233303.1221784-4-dmitry.baryshkov@linaro.org

drivers/gpu/drm/bridge/lontium-lt9611uxc.c

@@ -14,6 +14,7 @@
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/wait.h>
+#include <linux/workqueue.h>
 
 #include <sound/hdmi-codec.h>
 
@@ -36,6 +37,7 @@ struct lt9611uxc {
 	struct mutex ocm_lock;
 
 	struct wait_queue_head wq;
+	struct work_struct work;
 
 	struct device_node *dsi0_node;
 	struct device_node *dsi1_node;
@@ -52,6 +54,8 @@ struct lt9611uxc {
 
 	bool hpd_supported;
 	bool edid_read;
+	/* can be accessed from different threads, so protect this with ocm_lock */
+	bool hdmi_connected;
 	uint8_t fw_version;
 };
 
@@ -143,23 +147,41 @@ static irqreturn_t lt9611uxc_irq_thread_handler(int irq, void *dev_id)
 	if (irq_status)
 		regmap_write(lt9611uxc->regmap, 0xb022, 0);
 
-	lt9611uxc_unlock(lt9611uxc);
-
 	if (irq_status & BIT(0)) {
 		lt9611uxc->edid_read = !!(hpd_status & BIT(0));
 		wake_up_all(&lt9611uxc->wq);
 	}
 
 	if (irq_status & BIT(1)) {
-		if (lt9611uxc->connector.dev)
-			drm_kms_helper_hotplug_event(lt9611uxc->connector.dev);
-		else
-			drm_bridge_hpd_notify(&lt9611uxc->bridge, !!(hpd_status & BIT(1)));
+		lt9611uxc->hdmi_connected = hpd_status & BIT(1);
+		schedule_work(&lt9611uxc->work);
 	}
 
+	lt9611uxc_unlock(lt9611uxc);
+
 	return IRQ_HANDLED;
 }
 
+static void lt9611uxc_hpd_work(struct work_struct *work)
+{
+	struct lt9611uxc *lt9611uxc = container_of(work, struct lt9611uxc, work);
+	bool connected;
+
+	if (lt9611uxc->connector.dev)
+		drm_kms_helper_hotplug_event(lt9611uxc->connector.dev);
+	else {
+
+		mutex_lock(&lt9611uxc->ocm_lock);
+		connected = lt9611uxc->hdmi_connected;
+		mutex_unlock(&lt9611uxc->ocm_lock);
+
+		drm_bridge_hpd_notify(&lt9611uxc->bridge,
+				      connected ?
+				      connector_status_connected :
+				      connector_status_disconnected);
+	}
+}
+
 static void lt9611uxc_reset(struct lt9611uxc *lt9611uxc)
 {
 	gpiod_set_value_cansleep(lt9611uxc->reset_gpio, 1);
@@ -447,18 +469,21 @@ static enum drm_connector_status lt9611uxc_bridge_detect(struct drm_bridge *brid
 	struct lt9611uxc *lt9611uxc = bridge_to_lt9611uxc(bridge);
 	unsigned int reg_val = 0;
 	int ret;
-	int connected = 1;
+	bool connected = true;
+
+	lt9611uxc_lock(lt9611uxc);
 
 	if (lt9611uxc->hpd_supported) {
-		lt9611uxc_lock(lt9611uxc);
 		ret = regmap_read(lt9611uxc->regmap, 0xb023, &reg_val);
-		lt9611uxc_unlock(lt9611uxc);
 
 		if (ret)
 			dev_err(lt9611uxc->dev, "failed to read hpd status: %d\n", ret);
 		else
 			connected  = reg_val & BIT(1);
 	}
+	lt9611uxc->hdmi_connected = connected;
+
+	lt9611uxc_unlock(lt9611uxc);
 
 	return connected ?  connector_status_connected :
 				connector_status_disconnected;
@@ -931,6 +956,8 @@ retry:
 	lt9611uxc->fw_version = ret;
 
 	init_waitqueue_head(&lt9611uxc->wq);
+	INIT_WORK(&lt9611uxc->work, lt9611uxc_hpd_work);
+
 	ret = devm_request_threaded_irq(dev, client->irq, NULL,
 					lt9611uxc_irq_thread_handler,
 					IRQF_ONESHOT, "lt9611uxc", lt9611uxc);
@@ -967,6 +994,7 @@ static int lt9611uxc_remove(struct i2c_client *client)
 	struct lt9611uxc *lt9611uxc = i2c_get_clientdata(client);
 
 	disable_irq(client->irq);
+	flush_scheduled_work();
 	lt9611uxc_audio_exit(lt9611uxc);
 	drm_bridge_remove(&lt9611uxc->bridge);