drm/omap: dsi: allow DSI commands to be sent early

Panel drivers can send DSI commands in panel's prepare(), which happens
before the bridge's enable() is called. The OMAP DSI driver currently
only sets up the DSI interface at bridge's enable(), so prepare() cannot
be used to send DSI commands.

This patch fixes the issue by making it possible to enable the DSI
interface any time a command is about to be sent. Disabling the
interface is be done via delayed work.

Clarifications for the delayed disable work and the panel doing DSI
transactions:

bridge_enable: If the disable callback is called just before
bridge_enable takes the dsi_bus_lock, no problem, bridge_enable just
enables the interface again. If the callback is ran just after
bridge_enable's dsi_bus_unlock, no problem, dsi->video_enabled == true
so the callback does nothing.

bridge_disable: similar to bridge-enable, the callback won't do anything
if video_enabled == true, and after bridge-disable has turned the video
and the interface off, there's nothing to do for the callback.

omap_dsi_host_detach: this is called when the panel does
mipi_dsi_detach(), and we expect the panel to _not_ do any DSI
transactions after (or during) mipi_dsi_detatch(), so there are no
race conditions.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-85-tomi.valkeinen@ti.com

drivers/gpu/drm/omapdrm/dss/dsi.c

@@ -3500,6 +3500,9 @@ static void dsi_enable(struct dsi_data *dsi)
 
 	WARN_ON(!dsi_bus_is_locked(dsi));
 
+	if (WARN_ON(dsi->iface_enabled))
+		return;
+
 	mutex_lock(&dsi->lock);
 
 	r = dsi_runtime_get(dsi);
@@ -3512,6 +3515,8 @@ static void dsi_enable(struct dsi_data *dsi)
 	if (r)
 		goto err_init_dsi;
 
+	dsi->iface_enabled = true;
+
 	mutex_unlock(&dsi->lock);
 
 	return;
@@ -3527,6 +3532,9 @@ static void dsi_disable(struct dsi_data *dsi)
 {
 	WARN_ON(!dsi_bus_is_locked(dsi));
 
+	if (WARN_ON(!dsi->iface_enabled))
+		return;
+
 	mutex_lock(&dsi->lock);
 
 	dsi_sync_vc(dsi, 0);
@@ -3538,6 +3546,8 @@ static void dsi_disable(struct dsi_data *dsi)
 
 	dsi_runtime_put(dsi);
 
+	dsi->iface_enabled = false;
+
 	mutex_unlock(&dsi->lock);
 }
 
@@ -4226,10 +4236,12 @@ static ssize_t omap_dsi_host_transfer(struct mipi_dsi_host *host,
 
 	dsi_bus_lock(dsi);
 
-	if (dsi->video_enabled)
-		r = _omap_dsi_host_transfer(dsi, vc, msg);
-	else
-		r = -EIO;
+	if (!dsi->iface_enabled) {
+		dsi_enable(dsi);
+		schedule_delayed_work(&dsi->dsi_disable_work, msecs_to_jiffies(2000));
+	}
+
+	r = _omap_dsi_host_transfer(dsi, vc, msg);
 
 	dsi_bus_unlock(dsi);
 
@@ -4394,6 +4406,15 @@ static int omap_dsi_host_detach(struct mipi_dsi_host *host,
 	if (WARN_ON(dsi->dsidev != client))
 		return -EINVAL;
 
+	cancel_delayed_work_sync(&dsi->dsi_disable_work);
+
+	dsi_bus_lock(dsi);
+
+	if (dsi->iface_enabled)
+		dsi_disable(dsi);
+
+	dsi_bus_unlock(dsi);
+
 	omap_dsi_unregister_te_irq(dsi);
 	dsi->dsidev = NULL;
 	return 0;
@@ -4629,9 +4650,12 @@ static void dsi_bridge_enable(struct drm_bridge *bridge)
 	struct dsi_data *dsi = drm_bridge_to_dsi(bridge);
 	struct omap_dss_device *dssdev = &dsi->output;
 
+	cancel_delayed_work_sync(&dsi->dsi_disable_work);
+
 	dsi_bus_lock(dsi);
 
-	dsi_enable(dsi);
+	if (!dsi->iface_enabled)
+		dsi_enable(dsi);
 
 	dsi_enable_video_output(dssdev, VC_VIDEO);
 
@@ -4645,6 +4669,8 @@ static void dsi_bridge_disable(struct drm_bridge *bridge)
 	struct dsi_data *dsi = drm_bridge_to_dsi(bridge);
 	struct omap_dss_device *dssdev = &dsi->output;
 
+	cancel_delayed_work_sync(&dsi->dsi_disable_work);
+
 	dsi_bus_lock(dsi);
 
 	dsi->video_enabled = false;
@@ -4837,6 +4863,18 @@ static const struct soc_device_attribute dsi_soc_devices[] = {
 	{ /* sentinel */ }
 };
 
+static void omap_dsi_disable_work_callback(struct work_struct *work)
+{
+	struct dsi_data *dsi = container_of(work, struct dsi_data, dsi_disable_work.work);
+
+	dsi_bus_lock(dsi);
+
+	if (dsi->iface_enabled && !dsi->video_enabled)
+		dsi_disable(dsi);
+
+	dsi_bus_unlock(dsi);
+}
+
 static int dsi_probe(struct platform_device *pdev)
 {
 	const struct soc_device_attribute *soc;
@@ -4870,6 +4908,8 @@ static int dsi_probe(struct platform_device *pdev)
 	INIT_DEFERRABLE_WORK(&dsi->framedone_timeout_work,
 			     dsi_framedone_timeout_work_callback);
 
+	INIT_DEFERRABLE_WORK(&dsi->dsi_disable_work, omap_dsi_disable_work_callback);
+
 #ifdef DSI_CATCH_MISSING_TE
 	timer_setup(&dsi->te_timer, dsi_te_timeout, 0);
 #endif

drivers/gpu/drm/omapdrm/dss/dsi.h

@@ -394,6 +394,7 @@ struct dsi_data {
 	atomic_t do_ext_te_update;
 
 	bool te_enabled;
+	bool iface_enabled;
 	bool video_enabled;
 
 	struct delayed_work framedone_timeout_work;
@@ -443,6 +444,8 @@ struct dsi_data {
 
 	struct omap_dss_device output;
 	struct drm_bridge bridge;
+
+	struct delayed_work dsi_disable_work;
 };
 
 struct dsi_packet_sent_handler_data {