[Public]

-----Original Message-----
From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Sent: Wednesday, August 25, 2021 3:26 AM
To: Felipe Balbi <balbi@kernel.org>
Cc: Shah, Nehal-bakulchandra <redacted>;
gregkh@linuxfoundation.org; linux-usb@vger.kernel.org; linux-
kernel@vger.kernel.org; Liu, Kun [off-list ref]; Deucher,
Alexander [off-list ref]
Subject: Re: [RESEND PATCH 2/2] usb: dwc3: pci add property to allow user
space role switch

On Wed, Aug 25, 2021 at 10:01:05AM +0300, Heikki Krogerus wrote:

quoted

On Wed, Aug 25, 2021 at 08:55:41AM +0300, Felipe Balbi wrote:

quoted

Hi,

Nehal Bakulchandra Shah [off-list ref] writes:

quoted

For AMD platform there is a requirement to enable user space role
switch from host to device and device to host as customer platform
is not completely capable of OTG i.e. with type C controller it
does not have PD to support role switching. Hence, based ACPI/EC
interrupt role switch is triggered by the usemode script running in

background.

quoted

quoted

                   usermode ?

Couldn't you capture that ACPI/EC interrupt in kernel?

quoted

quoted

Signed-off-by: Nehal Bakulchandra Shah
[off-list ref]

I'm okay with this, just wondering if we need to Document the
property somewhere.

@Heikki, is there a place to document these private properties
that's not on DT binding document?

The build-in properties are not documented separately. I've always
tried to supply DT bindings for all new properties I've proposed.

In this case though, do we need the new property at all? Why not just
register a normal USB role switch on this platform? It can be either a
dummy role switch that only passes the user space input to dwc3, or,
perhaps ideally, it would also be a driver that captures that ACPI/EC
event/notification and then passes the information from it to dwc3.

Please ignore the above question. Sorry. Let me try again...

The question is: why not just capture that ACPI/EC "interrupt" in kernel and
then just use that information to set the dwc3 role switch?
No extra properties needed.

I'm not a USB expert, but I think the idea was to pop up a message asking the user what role they wanted when they plugged in USB cable?  Then based on their input, the role could be changed.

Alex