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

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Message-ID: <20170306012451.GB23305@b29397-desktop>
Date:   Mon, 6 Mar 2017 09:24:51 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        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 06:36:50AM -0800, Guenter Roeck wrote:
> On 03/02/2017 08:52 PM, Peter Chen wrote:
> >On Thu, Mar 02, 2017 at 08:29:07PM -0800, Guenter Roeck wrote:
> >>On 03/02/2017 07:35 PM, 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?
> >>
> >>If it helps, my primary test system is a HP Chromebook 13 G1.
> >>
> >>>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.
> >>
> >>I don't really understand "What interface you use when you receive
> >>this event". Can you explain ?
> >>
> >
> >I mean "How to trigger kernel USB controller driver do role switch?"
> >
> 
> I think this should be handled by the lower level driver. I am wide open
> to other ideas, though.
> 

Would you show me how it works at your test system if it is not
a private thing?

> >>>
> >>>Eg, if "data_role" has changed, the udev can echo "data_role" to
> >>>/sys/class/usb-dual-role/role
> >>>
> >>That sounds like a kernel event delivered to user space via udev or
> >>sysfs notification and returned back into the kernel through a sysfs
> >>attribute. Do I understand that correctly ?
> >>
> >
> >Yes.
> >
> 
> That doesn't sound like a good idea to me, and I don't see a technical reason
> to require it.
> 

I don't like it either, but current kernel has no ability to handle it
except you use hardware signal like extcon-gpio or controller id as
input pin to SoC handle this event.

-- 

Best Regards,
Peter Chen