linux-kernel - Re: [PATCH v2 1/6] device property: Helper to match multiple connections

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Message-ID: <YgOz6K55Oi2Si4pU@smile.fi.intel.com>
Date:   Wed, 9 Feb 2022 14:30:32 +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 v2 1/6] device property: Helper to match multiple
 connections

On Mon, Feb 07, 2022 at 07:19:39PM -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-C

USB Type-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

Type-C ?

> able to resolve them both.
> 
> Add a new API that allows this kind of lookup.
> 
> Given that the match() callback returns an opaque reference to something
> provided by the client it's not possible for the implementation to
> release the returned object and as such it's not possible to handle
> errors, which in turn means that it's not possible to query the number
> of elements or dynamically grow the results array. It's however expected
> that the number of matches will be reasonably low and that the worst
> case is known by the caller before hand.

...

> +	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)) {
> +			fwnode_handle_put(node);
> +			continue;
> +		}
> +
> +		ret = match(node, con_id, data);
> +		fwnode_handle_put(node);

> +

Redundant blank line (it seems the current style w/o this).
Ditto for the below function.

> +		if (ret)
> +			matches[count++] = ret;
> +	}

...

> +/**
> + * 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.

s/of/or/ ?

> + */
> +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)

!matches case may be still useful to get the count and allocate memory by
caller. Please, consider this case.

> +		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);

I haven't found any explanation what the difference between two counts. Also
can you define two count variables with distinct names and do something like

	count_A = ...

	matches += count;
	matches_len -= count;

	count_B = ...

	return count_A + count_B;

?

> +}

-- 
With Best Regards,
Andy Shevchenko