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

[Guenter Roeck]

On 03/07/2017 10:50 PM, Peter Chen wrote:
> > > > 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.
>
> I see, that means you have a hardware signal to notify role switch.

In our case the Type-C protocol manager (including alternate mode handling)
is implemented in an EC. The EC signals the extcon-cros_ec driver, which
in turn signals the phy driver as well as the DP driver. The Type-C class
is orthogonal; extcon-cros_ec will also register with the Type-C class code
once that is upstream.

As mentioned earlier, using extcon for signaling was the most convenient means
for us to pass events around. I am more than open to change it to a bus,
if that can be made to work - we'd have to keep in mind though that this code
already works without Type-C infrastructure and is for the most part already
upstream (the rk3399 code it ties into is upstream, and extcon-cros_ec has been
submitted as https://patchwork.kernel.org/patch/9583045/).

As for to how to handle alternate mode if the Type-C protocol manager
(TCPM) is implemented in the kernel - I have not yet implemented it yet,
but my thinking goes along the line described by Heikki in his last e-mail.

Note that we also have a kernel driver for FUSB302 which ties into my tcpm
driver. I'll have to check if that is public yet and if I or someone
else can publish it if there is interest.

Guenter