[PATCH v8 3/4] drm/atmel-hlcdc: iterate over all output endpoints

On Tue, 14 Aug 2018 17:05:29 +0200
Peter Rosin [off-list ref] wrote:

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@@ -77,13 +79,29 @@ static int atmel_hlcdc_attach_endpoint(struct drm_device *dev, int endpoint)

 int atmel_hlcdc_create_outputs(struct drm_device *dev)
 {
-    int endpoint, ret = 0;
-
-    for (endpoint = 0; !ret; endpoint++)
-            ret = atmel_hlcdc_attach_endpoint(dev, endpoint);
+    struct of_endpoint endpoint;
+    struct device_node *node = NULL;
+    int count = 0;
+    int ret = 0;
+
+    for_each_endpoint_of_node(dev->dev->of_node, node) {
+            of_graph_parse_endpoint(node, &endpoint);  

I'd really like to kill off of_graph_parse_endpoint, not add more
users (check the git history on this code). You should know what are
possible port and endpoint numbers, so iterate over those.  

So, add a comment to that effect in the docs of the of_graph_parse_endpoint
function.

How can the hlcdc driver know the actual number of endpoints? It's a
one-way signal path out from that port, and it can easily be routed to
1, 2, 3 or even more places. As shown above, forcing the endpoint id
to start at zero is a nuisance, and I don't see the point of it.

But I welcome suggestions on how to arrange the above dtsi/dts fragments
in a world where the endpoint id absolutely has to start at zero.  

Your dts file arrangement seems fine. Can't you just not exit the loop
on -ENODEV? IOW, just iterate til you find an enabled endpoint.  

That would regress cases where two (or more) endpoints are enabled
(which is currently supported). As I see it, the driver will have a
very hard time knowing when to stop iterating with any solution not
involving the equivalent of the functions for_each_endpoint_of_node
and of_graph_parse_endpoint. Open-coding of_graph_parse_endpoint just
to avoid it is a bit more than silly IMHO...

I agree, and actually, I think this is Rob who suggested to do what we
do here :-) (iterate from 0 to X, and stop as soon as
-ENODEV is returned).