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

[Guenter Roeck]

On 03/07/2017 12:57 AM, Heikki Krogerus wrote:
> On Tue, Mar 07, 2017 at 01:36:29AM +0000, Peter Chen wrote:
> > > 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?
>
> No (firmware programs the dual-role hw/registers), but never mind.
> That could be the case.
>
> > If it is correct, there is a notifier between type-C
> > and USB controller driver, how to define this notifier for non-ACPI platform?
>
> Once there is a platform with Type-C like that, the problem needs to
> be solved. However..
>
> > > 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.
>
> ..what ever the solution is, it really can't rely on user space.

... and, at least for our application, using extcon for the necessary notifications
works just fine.

Guenter