linux-kernel - Re: [PATCH v17 2/3] usb: USB Type-C connector class

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Message-ID: <20170306011551.GA23305@b29397-desktop>
Date:   Mon, 6 Mar 2017 09:15:51 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Oliver Neukum <oneukum@...e.com>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, Roger Quadros <rogerq@...com>,
        Jun Li <jun.li@....com>
Subject: Re: [PATCH v17 2/3] usb: USB Type-C connector class

On Fri, Mar 03, 2017 at 04:31:33PM +0200, Heikki Krogerus wrote:
> Hi Peter,
> 
> On Fri, Mar 03, 2017 at 11:35:29AM +0800, Peter Chen wrote:
> > On Tue, Feb 21, 2017 at 05:24:04PM +0300, Heikki Krogerus wrote:
> > > +/* --------------------------------------- */
> > > +/* Driver callbacks to report role updates */
> > > +
> > > +/**
> > > + * typec_set_data_role - Report data role change
> > > + * @port: The USB Type-C Port where the role was changed
> > > + * @role: The new data role
> > > + *
> > > + * This routine is used by the port drivers to report data role changes.
> > > + */
> > > +void typec_set_data_role(struct typec_port *port, enum typec_data_role role)
> > > +{
> > > +	if (port->data_role == role)
> > > +		return;
> > > +
> > > +	port->data_role = role;
> > > +	sysfs_notify(&port->dev.kobj, NULL, "data_role");
> > > +	kobject_uevent(&port->dev.kobj, KOBJ_CHANGE);
> > > +}
> > > +EXPORT_SYMBOL_GPL(typec_set_data_role);
> > > +
> > 
> > Hi Keikki,
> > 
> > Have you tested this interface with real dual-role controller/board?
> 
> Yes. Our boards are mostly USB dual-role capable.
> 
> > What interface you use when you receive this event to handle
> > dual-role switch? I am wonder if a common dual-role class is
> > needed, then we can have a common user utility.
> > 
> > Eg, if "data_role" has changed, the udev can echo "data_role" to
> > /sys/class/usb-dual-role/role
> 
> No. If the partner executes successfully for example DR_Swap message,
> the kernel has to take care everything that is needed for the role to
> be what ever was negotiated on its own. User space can't be involved
> with that.
> 

Would you give me an example how kernel handle this? How type-C event
triggers role switch?

-- 

Best Regards,
Peter Chen