drm/bridge: adv7511: Use work_struct to defer hotplug handing to out of irq context

I was recently seeing issues with EDID probing, where
the logic to wait for the EDID read bit to be set by the
IRQ wasn't happening and the code would time out and fail.

Digging deeper, I found this was due to the fact that
IRQs were disabled as we were running in IRQ context from
the HPD signal.

Thus this patch changes the logic to handle the HPD signal
via a work_struct so we can be out of irq context.

With this patch, the EDID probing on hotplug does not time
out.

Cc: David Airlie <airlied@linux.ie>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1484614372-15342-2-git-send-email-john.stultz@linaro.org

drivers/gpu/drm/bridge/adv7511/adv7511.h

@@ -318,6 +318,8 @@ struct adv7511 {
 	bool edid_read;
 
 	wait_queue_head_t wq;
+	struct work_struct hpd_work;
+
 	struct drm_bridge bridge;
 	struct drm_connector connector;
 

drivers/gpu/drm/bridge/adv7511/adv7511_drv.c

@@ -402,6 +402,13 @@ static bool adv7511_hpd(struct adv7511 *adv7511)
 	return false;
 }
 
+static void adv7511_hpd_work(struct work_struct *work)
+{
+	struct adv7511 *adv7511 = container_of(work, struct adv7511, hpd_work);
+
+	drm_helper_hpd_irq_event(adv7511->connector.dev);
+}
+
 static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)
 {
 	unsigned int irq0, irq1;
@@ -419,7 +426,7 @@ static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)
 	regmap_write(adv7511->regmap, ADV7511_REG_INT(1), irq1);
 
 	if (process_hpd && irq0 & ADV7511_INT0_HPD && adv7511->bridge.encoder)
-		drm_helper_hpd_irq_event(adv7511->connector.dev);
+		schedule_work(&adv7511->hpd_work);
 
 	if (irq0 & ADV7511_INT0_EDID_READY || irq1 & ADV7511_INT1_DDC_ERROR) {
 		adv7511->edid_read = true;
@@ -1070,6 +1077,8 @@ static int adv7511_probe(struct i2c_client *i2c, const struct i2c_device_id *id)
 			goto err_i2c_unregister_edid;
 	}
 
+	INIT_WORK(&adv7511->hpd_work, adv7511_hpd_work);
+
 	if (i2c->irq) {
 		init_waitqueue_head(&adv7511->wq);