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Date: Tue, 28 Dec 2021 10:42:02 -0800
From: Bjorn Andersson <bjorn.andersson@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Kishon Vijay Abraham I <kishon@...com>,
Vinod Koul <vkoul@...nel.org>,
Rob Herring <robh+dt@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Hans de Goede <hdegoede@...hat.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-usb@...r.kernel.org
Subject: 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
> <bjorn.andersson@...aro.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@...aro.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
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