[PATCH v2 2/2] drm/bridge: parade-ps8640: Handle DP AUX more properly

[Douglas Anderson <dianders@chromium.org>]

While it works, for the most part, to assume that the panel has
finished probing when devm_of_dp_aux_populate_ep_devices() returns,
it's a bit fragile. This is talked about at length in commit
a1e3667a9835 ("drm/bridge: ti-sn65dsi86: Promote the AUX channel to
its own sub-dev").

When reviewing the ps8640 code, I managed to convince myself that it
was OK not to worry about it there and that maybe it wasn't really
_that_ fragile. However, it turns out that it really is. Simply
hardcoding panel_edp_probe() to return -EPROBE_DEFER was enough to put
the boot process into an infinite loop. I believe this manages to trip
the same issues that we used to trip with the main MSM code where
something about our actions trigger Linux to re-probe previously
deferred devices right away and each time we try again we re-trigger
Linux to re-probe.

Let's fix this using the callback introduced in the patch ("drm/dp:
Callbacks to make it easier for drivers to use DP AUX bus properly").
When using the new callback, we have to be a little careful. The
probe_done() callback is no longer (always) called in the context of
our probe routine. That means we can't rely on being able to return
-EPROBE_DEFER from it. We re-jigger the order of things a bit to
account for that.

With this change, the device still boots (though obviously the panel
doesn't come up) if I force panel-edp to always return
-EPROBE_DEFER. If I fake it and make the panel probe exactly once it
also works.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v2:
- Rewrote atop new method introduced by patch #1.

 drivers/gpu/drm/bridge/parade-ps8640.c | 77 +++++++++++++++++---------
 1 file changed, 52 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
index edb939b14c04..68131ca91eac 100644
--- a/drivers/gpu/drm/bridge/parade-ps8640.c
+++ b/drivers/gpu/drm/bridge/parade-ps8640.c
@@ -104,6 +104,7 @@ struct ps8640 {
 	struct gpio_desc *gpio_powerdown;
 	struct device_link *link;
 	bool pre_enabled;
+	bool bridge_added;
 };
 
 static const struct regmap_config ps8640_regmap_config[] = {
@@ -537,12 +538,11 @@ static const struct drm_bridge_funcs ps8640_bridge_funcs = {
 	.pre_enable = ps8640_pre_enable,
 };
 
-static int ps8640_bridge_host_attach(struct device *dev, struct ps8640 *ps_bridge)
+static int ps8640_bridge_get_dsi_resources(struct device *dev, struct ps8640 *ps_bridge)
 {
 	struct device_node *in_ep, *dsi_node;
 	struct mipi_dsi_device *dsi;
 	struct mipi_dsi_host *host;
-	int ret;
 	const struct mipi_dsi_device_info info = { .type = "ps8640",
 						   .channel = 0,
 						   .node = NULL,
@@ -577,17 +577,44 @@ static int ps8640_bridge_host_attach(struct device *dev, struct ps8640 *ps_bridg
 	dsi->format = MIPI_DSI_FMT_RGB888;
 	dsi->lanes = NUM_MIPI_LANES;
 
-	ret = devm_mipi_dsi_attach(dev, dsi);
+	return 0;
+}
+
+static int ps8640_bridge_link_panel(struct drm_dp_aux *aux)
+{
+	struct ps8640 *ps_bridge = aux_to_ps8640(aux);
+	struct device *dev = aux->dev;
+	struct device_node *np = dev->of_node;
+	int ret;
+
+	/*
+	 * NOTE about returning -EPROBE_DEFER from this function: if we
+	 * return an error (most relevant to -EPROBE_DEFER) it will only
+	 * be passed out to ps8640_probe() if we don't have our panel
+	 * under the "aux-bus". That should be fine because if the panel is
+	 * under "aux-bus" it's guaranteed to have probed by the time this
+	 * function has been called.
+	 */
+
+	/* port@1 is ps8640 output port */
+	ps_bridge->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
+	if (IS_ERR(ps_bridge->panel_bridge))
+		return PTR_ERR(ps_bridge->panel_bridge);
+
+	drm_bridge_add(&ps_bridge->bridge);
+
+	ret = devm_mipi_dsi_attach(dev, ps_bridge->dsi);
 	if (ret)
-		return ret;
+		drm_bridge_remove(&ps_bridge->bridge);
+	else
+		ps_bridge->bridge_added = true;
 
-	return 0;
+	return ret;
 }
 
 static int ps8640_probe(struct i2c_client *client)
 {
 	struct device *dev = &client->dev;
-	struct device_node *np = dev->of_node;
 	struct ps8640 *ps_bridge;
 	int ret;
 	u32 i;
@@ -628,6 +655,14 @@ static int ps8640_probe(struct i2c_client *client)
 	if (!ps8640_of_panel_on_aux_bus(&client->dev))
 		ps_bridge->bridge.ops = DRM_BRIDGE_OP_EDID;
 
+	/*
+	 * Get MIPI DSI resources early. These can return -EPROBE_DEFER so
+	 * we want to get them out of the way sooner.
+	 */
+	ret = ps8640_bridge_get_dsi_resources(&client->dev, ps_bridge);
+	if (ret)
+		return ret;
+
 	ps_bridge->page[PAGE0_DP_CNTL] = client;
 
 	ps_bridge->regmap[PAGE0_DP_CNTL] = devm_regmap_init_i2c(client, ps8640_regmap_config);
@@ -670,31 +705,23 @@ static int ps8640_probe(struct i2c_client *client)
 	if (ret)
 		return ret;
 
-	devm_of_dp_aux_populate_ep_devices(&ps_bridge->aux);
-
-	/* port@1 is ps8640 output port */
-	ps_bridge->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
-	if (IS_ERR(ps_bridge->panel_bridge))
-		return PTR_ERR(ps_bridge->panel_bridge);
-
-	drm_bridge_add(&ps_bridge->bridge);
-
-	ret = ps8640_bridge_host_attach(dev, ps_bridge);
-	if (ret)
-		goto err_bridge_remove;
-
-	return 0;
-
-err_bridge_remove:
-	drm_bridge_remove(&ps_bridge->bridge);
-	return ret;
+	/*
+	 * Kick off the probe for our panel if it's on the dp-aux bus.
+	 * If the panel is on the aux bus ps8640_bridge_link_panel() will
+	 * get called when it finishes probing. If the panel is an old-style
+	 * platform device ps8640_bridge_link_panel() will be called directly
+	 * and its return value will be the return value of our function.
+	 */
+	return devm_of_dp_aux_populate_ep_device(&ps_bridge->aux,
+						 ps8640_bridge_link_panel);
 }
 
 static int ps8640_remove(struct i2c_client *client)
 {
 	struct ps8640 *ps_bridge = i2c_get_clientdata(client);
 
-	drm_bridge_remove(&ps_bridge->bridge);
+	if (ps_bridge->bridge_added)
+		drm_bridge_remove(&ps_bridge->bridge);
 
 	return 0;
 }
-- 
2.36.0.464.gb9c8b46e94-goog