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From: Guenter Roeck <linux@roeck-us.net>
Newsgroups: linux.kernel
Subject: Re: [PATCHv8 1/2] usb: USB Type-C connector class
Date: Thu, 08 Sep 2016 22:10:02 +0200
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Xref: csiph.com linux.kernel:1479479

On Thu, Sep 01, 2016 at 02:49:47PM +0300, Heikki Krogerus wrote:
> The purpose of USB Type-C connector class is to provide
> unified interface for the user space to get the status and
> basic information about USB Type-C connectors on a system,
> control over data role swapping, and when the port supports
> USB Power Delivery, also control over power role swapping
> and Alternate Modes.
> 
> Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> ---
... 

> +
> +static int sysfs_strmatch(const char * const *array, size_t n, const char *str)
> +{
> +	const char *item;
> +	int index;
> +
> +	for (index = 0; index < n; index++) {
> +		item = array[index];
> +		if (!item)
> +			break;
> +		if (!sysfs_streq(item, str))

This doesn't work ... sysfs_streq() returns true if there is a match,
so the "!" is wrong.

> +			return index;
> +	}
> +
> +	return -EINVAL;
> +}
> +
[ ... ]
> +
> +static ssize_t
> +preferred_role_store(struct device *dev, struct device_attribute *attr,
> +		     const char *buf, size_t size)
> +{
> +	struct typec_port *port = to_typec_port(dev);
> +	enum typec_role role;
> +	int ret;
> +
> +	if (port->cap->type != TYPEC_PORT_DRP) {
> +		dev_dbg(dev, "Preferred role only supported with DRP ports\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (!port->cap->try_role) {
> +		dev_dbg(dev, "Setting preferred role not supported\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	ret = sysfs_strmatch(typec_roles, ARRAY_SIZE(typec_roles), buf);
> +	if (ret < 0) {
> +		port->prefer_role = -1;
> +		return size;

Are you sure about that ? It is kind of unusual to accept "bad" strings.
Why not return -EINVAL ?

> +	}
> +
> +	role = ret;
> +
> +	ret = port->cap->try_role(port->cap, role);
> +	if (ret)
> +		return ret;
> +
> +	port->prefer_role = role;
> +	return size;
> +}
> +
[ ... ]
> +
> +static ssize_t supported_accessory_modes_show(struct device *dev,
> +					      struct device_attribute *attr,
> +					      char *buf)
> +{
> +	struct typec_port *port = to_typec_port(dev);
> +	ssize_t ret = 0;
> +	int i;
> +
> +	if (!port->cap->accessory[0])

You probably want 
	if (!port->cap->accessory)
here. Otherwise the check is quite pointless (and crashes if the pointer
is NULL).

> +		return 0;
> +
> +	for (i = 0; port->cap->accessory[i]; i++)
> +		ret += sprintf(buf + ret, "%s\n",
> +			       typec_accessory_modes[port->cap->accessory[i]]);
> +	return ret;
> +}
> +static DEVICE_ATTR_RO(supported_accessory_modes);
> +

Guenter