linux-kernel - Re: [RFC PATCHv3] usb: USB Type-C Connector Class

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Message-ID: <20160613074939.GB13291@kuha.fi.intel.com>
Date:	Mon, 13 Jun 2016 10:49:39 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Oliver Neukum <oneukum@...e.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [RFC PATCHv3] usb: USB Type-C Connector Class

On Sat, Jun 11, 2016 at 11:03:53AM -0700, Guenter Roeck wrote:
> On 06/11/2016 12:05 AM, Oliver Neukum wrote:
> > On Fri, 2016-06-10 at 17:34 +0300, Heikki Krogerus wrote:
> > > +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;
> > > +
> > > +       mutex_lock(&port->lock);
> > > +
> > > +       if (port->cap->type != TYPEC_PORT_DRP) {
> > > +               dev_dbg(dev, "Try.SRC/SNK only supported with DRP
> > > ports\n");
> > > +               ret = -EOPNOTSUPP;
> > > +               goto out;
> > > +       }
> > 
> > I think Try.SNK with an UFP should fail differently from
> > Try.SRC and vice versa.
> > 
> 
> I think the message should not even mention Try.src or Try.snk
> in the first place, since both are optional and really orthogonal
> to how the role is set (it can also be changed with pd messages).
> On top of that, the specification states that Try.{src/snk} are
> optional if there is no PD support, and NA if PD is supported
> (see table 4.10). Kind of interesting, and I wonder how this
> is supposed to be implemented in practice, since Try.{src/snk}
> runs before it is established that/if the partner supports PD.
> 
> A better message would be something like "Setting preferred
> role only supported with DRP ports", and leave implementation
> details to the port driver.

Works for me.

Thanks,

-- 
heikki