linux-kernel - Re: [PATCHv8 1/2] usb: USB Type-C connector class

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Date:   Fri, 9 Sep 2016 10:36:00 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Oliver Neukum <oneukum@...e.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Vincent Palatin <vpalatin@...omium.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCHv8 1/2] usb: USB Type-C connector class

On Thu, Sep 08, 2016 at 01:04:29PM -0700, Guenter Roeck wrote:
> 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@...ux.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.

Oh no! I've been testing (stupidly) with a patch on top where I move
this function to lib/string.c (I guess I had this correctly in that).
Sorry about this.

> > +			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 ?

I'm considering a "bad" string as clearing the preference. I did
explain this in the ABI document. But I suppose it's better to define
a specific string also for clearing. I'll change this.

> > +	}
> > +
> > +	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).

OK.


Thanks,

-- 
heikki