Re: [PATCH v4 1/7] device property: Helper to match multiple connections

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>,
	Daniel Scally <djrscally@gmail.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Hans de Goede <hdegoede@redhat.com>,
	linux-usb@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Subject: Re: [PATCH v4 1/7] device property: Helper to match multiple connections
Date: Mon, 7 Mar 2022 12:05:56 +0200	[thread overview]
Message-ID: <YiXZBMG7cK6Cm7wP@smile.fi.intel.com> (raw)
In-Reply-To: <20220307034040.1111107-1-bjorn.andersson@linaro.org>

On Sun, Mar 06, 2022 at 07:40:34PM -0800, 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
> Type-C connector. In this case the connector needs to belong to a graph
> with multiple matching remote endpoints, and the Type-C controller needs
> to be able to resolve them both.
> 
> Add a new API that allows this kind of lookup.

Thanks for the update!

First of all, I have noticed that subject misses the verb, something like Add
or Introduce.

...

> +/**
> + * 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

(Optional) array...

> + * @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.

> + * If @matches is NULL @matches_len is ignored and the total number of resolved
> + * matches is returned.

I would require matches_len to be 0, see below.

> + * Return: Number of matches resolved, or 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_graph;
> +	unsigned int count_ref;
> +
> +	if (!fwnode || !match)
> +		return -EINVAL;
> +
> +	count_graph = fwnode_graph_devcon_matches(fwnode, con_id, data, match,
> +						  matches, matches_len);

> +	if (matches) {
> +		matches += count_graph;
> +		matches_len -= count_graph;
> +	}

So, the valid case is matches != NULL and matches_len == 0. For example, when
we have run something previously on the buffer and it becomes full.

In this case we have carefully handle this case.

	if (matches) {
		matches += count_graph;
		if (matches_len)
			matches_len -= count_graph;
	}

Seems it can be also

	if (matches)
		matches += count_graph;

	if (matches_len)
		matches_len -= count_graph;

That said, do we have a test cases for this?

> +	count_ref = fwnode_devcon_matches(fwnode, con_id, data, match,
> +					  matches, matches_len);
> +
> +	return count_graph + count_ref;
> +}

-- 
With Best Regards,
Andy Shevchenko