linux-kernel - Re: [PATCHv12 2/3] usb: USB Type-C connector class

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Date:   Wed, 23 Nov 2016 21:12:04 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     Badhri Jagan Sridharan <badhri@...gle.com>,
        Oliver Neukum <oneukum@...e.com>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCHv12 2/3] usb: USB Type-C connector class

Hello Heikki,

On 11/22/2016 06:11 AM, Heikki Krogerus wrote:
[ ... ]
> +
> +struct typec_port *typec_register_port(struct device *dev,
> +				       const struct typec_capability *cap)
> +{
> +	struct typec_port *port;
> +	int ret;
> +	int id;
> +
> +	port = kzalloc(sizeof(*port), GFP_KERNEL);
> +	if (!port)
> +		return ERR_PTR(-ENOMEM);
> +
> +	id = ida_simple_get(&typec_index_ida, 0, 0, GFP_KERNEL);
> +	if (id < 0) {
> +		kfree(port);
> +		return ERR_PTR(id);
> +	}
> +
> +	port->prefer_role = TYPEC_NO_PREFERRED_ROLE;
> +

Following up on this:

In our implementation, the default preferred role is determined by the
low level driver (as, in my understanding, is suggested by the standard).
This means that the ABI will report "no preferred role", unless user space
overwrites it, even though there _is_ in fact a preferred role, and the
low level driver will execute try.src or try.snk based on that role.

It might make sense to add the preferred role to struct typec_capability
and get the initial value from there. If a low level driver does not want
to specify it, it can easily set its value to TYPEC_NO_PREFERRED_ROLE.

Thanks,
Guenter