linux-kernel - Re: [PATCH v3 1/6] device property: Helper to match multiple connections

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Date:   Fri, 4 Mar 2022 14:54:21 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v3 1/6] device property: Helper to match multiple
 connections

On Thu, Mar 03, 2022 at 02:33:46PM -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.

...

> +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 && matches) {
> +			fwnode_handle_put(ep);
> +			return count;
> +		}

Wouldn't be the same as

		if (count >= matches_len) {
			fwnode_handle_put(ep);
			break;
		}

?

> +		node = fwnode_graph_get_remote_port_parent(ep);
> +		if (!fwnode_device_is_available(node)) {
> +			fwnode_handle_put(node);
> +			continue;
> +		}
> +
> +		ret = match(node, con_id, data);
> +		fwnode_handle_put(node);
> +		if (ret) {
> +			if (matches)
> +				matches[count] = ret;
> +			count++;
> +		}
> +	}
> +	return count;
> +}

...

> +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;
> +	unsigned int i;
> +	void *ret;
> +
> +	for (i = 0; ; i++) {

> +		if (count >= matches_len && matches)
> +			return count;

Ditto.

> +		node = fwnode_find_reference(fwnode, con_id, i);
> +		if (IS_ERR(node))
> +			break;
> +
> +		ret = match(node, NULL, data);
> +		fwnode_handle_put(node);
> +		if (ret) {
> +			if (matches)
> +				matches[count] = ret;
> +			count++;
> +		}
> +	}
> +
> +	return count;
> +}

...

> +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);

> +	matches += count_graph;
> +	matches_len -= count_graph;

No, won't work when matches == NULL.

Also, matches_len is expected to be 0 in that case (or at least being ignored,
check with vsnprintf() behaviour in similar case).

So, something like this, perhaps

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

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


-- 
With Best Regards,
Andy Shevchenko