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

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Date:   Tue, 7 Mar 2017 01:36:29 +0000
From:   Peter Chen <peter.chen@....com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Peter Chen <hzpeterchen@...il.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-kernel@...r.kernel.org>,
        "linux-usb@...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 Mon, Mar 06, 2017 at 09:15:51AM +0800, Peter Chen wrote:
>> > > 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?
>
>On our boards, the firmware or EC (or ACPI) configures the hardware as needed
>and also notifies the components using ACPI if needed. It's often not even possible to
>directly configure the components/hardware for a particular role.
>

You mean type-C trigger an ACPI event, and this ACPI event can notify related
USB controller driver doing role switch? If it is correct, there is a notifier between type-C
and USB controller driver, how to define this notifier for non-ACPI platform? 

>I'm not commenting on Roger's dual role patch series, but I don't really think it should
>be mixed with Type-C. USB Type-C and USB Power Delivery define their own ways
>of handling the roles, and they are not limited to the data role only. Things like OTG
>for example will, and actually can not be supported. With Type-C we will have
>competing state machines compared to OTG. The dual-role framework may be
>useful on systems that provide more traditional connectors, which possibly have the
>ID-pin like micro-AB, and possibly also support OTG. It can also be something that
>exist in parallel with the Type-C class, but there just can not be any dependencies
>between the two.
>

Yes, there are two independent things. But if the kernel doesn't have a notifier between
type-C message sender (type-c class) and message receiver (like USB controller driver
for role switch or other drivers for alternate mode message), we had to find some ways at
userspace.

Peter