On Mon, Jan 29, 2024 at 03:02:19PM +0200, Laurent Pinchart wrote:

On Mon, Jan 29, 2024 at 02:29:22PM +0200, Tomi Valkeinen wrote:

quoted

On 29/01/2024 02:54, Kuninori Morimoto wrote:

quoted

We already have of_graph_get_next_endpoint(), but it is not intuitive
to use.

(X)	node {
(Y)		ports {
			port@0 { endpoint { remote-endpoint = ...; };};
(A1)			port@1 { endpoint { remote-endpoint = ...; };
(A2)				 endpoint { remote-endpoint = ...; };};
(B)			port@2 { endpoint { remote-endpoint = ...; };};
		};
	};

For example, if I want to handle port@1's 2 endpoints (= A1, A2),
I want to use like below

	A1 = of_graph_get_next_endpoint(port1, NULL);
	A2 = of_graph_get_next_endpoint(port1, A1);

But 1st one will be error, because of_graph_get_next_endpoint() requested
"parent" means "node" (X) or "ports" (Y), not "port".
Below are OK

	of_graph_get_next_endpoint(node,  NULL); // node/ports/port@0/endpoint
	of_graph_get_next_endpoint(ports, NULL); // node/ports/port@0/endpoint

In other words, we can't handle A1/A2 directly via
of_graph_get_next_endpoint() so far.

There is another non intuitive behavior on of_graph_get_next_endpoint().
In case of if I could get A1 pointer for some way, and if I want to
handle port@1 things, I would like use it like below

	/*
	 * "endpoint" is now A1, and handle port1 things here,
	 * but we don't know how many endpoints port1 has.
	 *
	 * Because "endpoint" is non NULL, we can use port1
	 * as of_graph_get_next_endpoint(port1, xxx)
	 */
	do {
		/* do something for port1 specific things here */
	} while (endpoint = of_graph_get_next_endpoint(port1, endpoint))

But it also not worked as I expected.
I expect it will be A1 -> A2 -> NULL,
but      it will be A1 -> A2 -> B,    because of_graph_get_next_endpoint()
will fetch endpoint beyond the port.

It is not useful on generic driver like Generic Sound Card.
It uses of_get_next_child() instead for now, but it is not intuitive,
and not check node name (= "endpoint").

To handle endpoint more intuitive, create of_graph_get_next_endpoint_raw()

	of_graph_get_next_endpoint_raw(port1, NULL); // A1
	of_graph_get_next_endpoint_raw(port1, A1);   // A2
	of_graph_get_next_endpoint_raw(port1, A2);   // NULL

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
---
  drivers/of/property.c    | 26 +++++++++++++++++++++++++-
  include/linux/of_graph.h |  2 ++
  2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index 14ffd199c9b1..37dbb1b0e742 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c

@@ -667,6 +667,30 @@ struct device_node *of_graph_get_next_port(const struct device_node *parent,
  }
  EXPORT_SYMBOL(of_graph_get_next_port);
  
+/**
+ * of_graph_get_next_endpoint_raw() - get next endpoint node

How about "of_graph_get_next_port_endpoint()"?

We may want to also rename the existing of_graph_get_next_endpoint()
function to of_graph_next_dev_endpoint() then. It would be a tree-wide
patch, which is always annoying to get reviewed and merged, so if Rob
would prefer avoiding the rename, I'm fine with that.

I think we should get rid of or minimize of_graph_get_next_endpoint() in 
its current form. In general, drivers should be asking for a specific 
port number because their function is fixed in the binding. Iterating 
over endpoints within a port is okay as that's usually a selecting 1 of 
N operation. 

Most cases are in the form of of_graph_get_next_endpoint(dev, NULL) 
which is equivalent to of_graph_get_endpoint_by_regs(dev, 0, 0). 
Technically, -1 instead of 0 is equivalent, but I'd argue is sloppy and 
wrong.

I also added of_graph_get_remote_node() for this reason and cleaned a 
lot of these (in DRM) up some time ago. Because in the end, a driver 
generally just wants the remote device it is connected to and details of 
parsing the graph should be mostly opaque.

Wouldn't something like this work for this case:

#define for_each_port_endpoint_of_node(parent, port, child) \
	for (child = of_graph_get_endpoint_by_regs(parent, port, -1); child != NULL; \
	     child = of_get_next_child(parent, child))

Rob