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

[Bjorn Andersson <bjorn.andersson@linaro.org>]

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

> On Tue, 28 Dec 2021 at 20:03, Bjorn Andersson
> <bjorn.andersson@linaro.org> wrote:
> >
> > On Tue 28 Dec 05:09 PST 2021, Dmitry Baryshkov wrote:
> >
> > > On 28/12/2021 08:21, Bjorn Andersson wrote:
> > > > 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 <bjorn.andersson@linaro.org>
> > > > ---
> > > >   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

> >
> > Regards,
> > Bjorn
> >
> > > > +
> > > >   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.
> > >
> > > >   /**
> > > >    * 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