Re: [PATCH 3/8] device property: Helper to match multiple connections

On Tue 28 Dec 10:24 PST 2021, Dmitry Baryshkov wrote:

On Tue, 28 Dec 2021 at 20:03, Bjorn Andersson
[off-list ref] wrote:

quoted

On Tue 28 Dec 05:09 PST 2021, Dmitry Baryshkov wrote:

quoted

On 28/12/2021 08:21, Bjorn Andersson wrote:

quoted

In some cases multiple connections with the same connection id
needs to be resolved from a fwnode graph.

One such example is when separate hardware is used for performing muxing and/or
orientation switching of the SuperSpeed and SBU lines in a USB-C
connector. In this case the connector needs to belong to a graph with
multiple matching remote endpoints, and the TypeC controller needs to be
able to resolve them both.

Add a new API that allows this kind of lookup.

Signed-off-by: Bjorn Andersson <redacted>
---
  drivers/base/property.c  | 94 ++++++++++++++++++++++++++++++++++++++++
  include/linux/property.h |  5 +++
  2 files changed, 99 insertions(+)

diff --git a/drivers/base/property.c b/drivers/base/property.c
index cbe4fa298413..0aa0296fd991 100644
--- a/drivers/base/property.c
+++ b/drivers/base/property.c

@@ -1180,6 +1180,36 @@ fwnode_graph_devcon_match(struct fwnode_handle *fwnode, const char *con_id,
    return NULL;
  }
+static unsigned int fwnode_graph_devcon_matches(struct fwnode_handle *fwnode,
+                                           const char *con_id, void *data,
+                                           devcon_match_fn_t match,
+                                           void **matches,
+                                           unsigned int matches_len)
+{
+   struct fwnode_handle *node;
+   struct fwnode_handle *ep;
+   unsigned int count = 0;
+   void *ret;
+
+   fwnode_graph_for_each_endpoint(fwnode, ep) {
+           if (count >= matches_len) {
+                   fwnode_handle_put(ep);
+                   return count;
+           }
+
+           node = fwnode_graph_get_remote_port_parent(ep);
+           if (!fwnode_device_is_available(node))
+                   continue;
+
+           ret = match(node, con_id, data);
+           fwnode_handle_put(node);
+
+           if (ret)
+                   matches[count++] = ret;
+   }
+   return count;
+}

This API doesn't let it's user know if there are more matches found in the
device tree or not. I'd suggest to add 'count' mode that would return the
amount of found matches if (matches == NULL) && (matches_len == 0).

Unfortunately in this code path we don't know how to "free" the objects
returned by match(), e.g. see how typec_switch_match() returns wrapper
of a refcounted device.

So we must return all the match results to the caller to it can free
things up based on its knowledge of what matches[] actually contains..

Ugh. Then we should probably return -E2BIG, -ENOSPC or any other such error.
Another option might be to split match into match & map functions,
first one returning bool and second one returning actual corresponding
object..

If I get an errno back from a function like this I generally expect this
kind of API to have done the cleanup for me, which can't be done. So I
fear that it would be more error prone than the current proposal - which
potentially might (silently) fail to detect that you have 4+ orientation
switches attached to your USB port.

My imagination doesn't isn't able to come up with a large enough
of_graph where the client would need to provide an matches array that's
larger than what would fit on the stack. Perhaps someone can provide a
real use case where it would be necessary to support arbitrary sizes of
matches[]?

Regards,
Bjorn

quoted

Regards,
Bjorn

quoted

quoted

+
  static void *
  fwnode_devcon_match(struct fwnode_handle *fwnode, const char *con_id,
                void *data, devcon_match_fn_t match)

@@ -1202,6 +1232,35 @@ fwnode_devcon_match(struct fwnode_handle *fwnode, const char *con_id,
    return NULL;
  }
+static unsigned int fwnode_devcon_matches(struct fwnode_handle *fwnode,
+                                     const char *con_id, void *data,
+                                     devcon_match_fn_t match,
+                                     void **matches,
+                                     unsigned int matches_len)
+{
+   struct fwnode_handle *node;
+   unsigned int count = 0;
+   void *ret;
+   int i;
+
+   for (i = 0; ; i++) {
+           if (count >= matches_len)
+                   return count;
+
+           node = fwnode_find_reference(fwnode, con_id, i);
+           if (IS_ERR(node))
+                   break;
+
+           ret = match(node, NULL, data);
+           fwnode_handle_put(node);
+
+           if (ret)
+                   matches[count++] = ret;
+   }
+
+   return count;
+}
+

Same comment applies.

quoted

  /**
   * fwnode_connection_find_match - Find connection from a device node
   * @fwnode: Device node with the connection

@@ -1229,3 +1288,38 @@ void *fwnode_connection_find_match(struct fwnode_handle *fwnode,
    return fwnode_devcon_match(fwnode, con_id, data, match);
  }
  EXPORT_SYMBOL_GPL(fwnode_connection_find_match);
+
+/**
+ * fwnode_connection_find_matches - Find connections from a device node
+ * @fwnode: Device node with the connection
+ * @con_id: Identifier for the connection
+ * @data: Data for the match function
+ * @match: Function to check and convert the connection description
+ * @matches: Array of pointers to fill with matches
+ * @matches_len: Length of @matches
+ *
+ * Find up to @matches_len connections with unique identifier @con_id between
+ * @fwnode and other device nodes. @match will be used to convert the
+ * connection description to data the caller is expecting to be returned
+ * through the @matches array.
+ *
+ * Return: Number of matches resolved, of negative errno.
+ */
+int fwnode_connection_find_matches(struct fwnode_handle *fwnode,
+                              const char *con_id, void *data,
+                              devcon_match_fn_t match,
+                              void **matches, unsigned int matches_len)
+{
+   unsigned int count;
+
+   if (!fwnode || !match || !matches)
+           return -EINVAL;
+
+   count = fwnode_graph_devcon_matches(fwnode, con_id, data, match,
+                                       matches, matches_len);
+
+   return count + fwnode_devcon_matches(fwnode, con_id, data, match,
+                                        matches + count,
+                                        matches_len - count);
+}
+EXPORT_SYMBOL_GPL(fwnode_connection_find_matches);

diff --git a/include/linux/property.h b/include/linux/property.h
index 16f736c698a2..59484ccb260e 100644
--- a/include/linux/property.h
+++ b/include/linux/property.h

@@ -444,6 +444,11 @@ static inline void *device_connection_find_match(struct device *dev,
    return fwnode_connection_find_match(dev_fwnode(dev), con_id, data, match);
  }
+int fwnode_connection_find_matches(struct fwnode_handle *fwnode,
+                              const char *con_id, void *data,
+                              devcon_match_fn_t match,
+                              void **matches, unsigned int matches_len);
+
  /* -------------------------------------------------------------------------- */
  /* Software fwnode support - when HW description is incomplete or missing */

--
With best wishes
Dmitry

-- 
With best wishes
Dmitry

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