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

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Date:   Fri, 3 Mar 2017 06:36:50 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Peter Chen <hzpeterchen@...il.com>
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 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.

>>>
>>> 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.

Thanks,
Guenter