Subject: Re: [PATCH v13 3/4] gpio: rpmsg: add generic rpmsg GPIO driver

From: Mathieu Poirier <[email-masked]>
Date: Wed, 29 Apr 2026 09:41:46 -0600

On Tue, Apr 28, 2026 at 03:24:59PM +0000, Shenwei Wang wrote:
> 
> 
> > -----Original Message-----
> > From: Andrew Lunn <[email-masked]>
> > Sent: Monday, April 27, 2026 3:49 PM
> > To: Shenwei Wang <[email-masked]>
> > Cc: Padhi, Beleswar <[email-masked]>; Linus Walleij <[email-masked]>;
> > Bartosz Golaszewski <[email-masked]>; Jonathan Corbet <[email-masked]>;
> > Rob Herring <[email-masked]>; Krzysztof Kozlowski <[email-masked]>;
> > Conor Dooley <[email-masked]>; Bjorn Andersson
> > <[email-masked]>; Mathieu Poirier <[email-masked]>; Frank Li
> > <[email-masked]>; Sascha Hauer <[email-masked]>; Shuah Khan
> > <[email-masked]>; [email-masked]; linux-
> > [email-masked]; [email-masked]; Pengutronix Kernel Team
> > <[email-masked]>; Fabio Estevam <[email-masked]>; Peng Fan
> > <[email-masked]>; [email-masked]; linux-
> > [email-masked]; [email-masked]; linux-arm-
> > [email-masked]; dl-linux-imx <[email-masked]>; Bartosz
> > Golaszewski <[email-masked]>
> > Subject: [EXT] Re: [PATCH v13 3/4] gpio: rpmsg: add generic rpmsg GPIO driver
> > > > struct virtio_gpio_response {
> > > >         __u8 status;
> > > >         __u8 value;
> > > > };
> > 
> > > It is the same message format. Please see the message definition
> > (GET_DIRECTION) below:
> > 
> > > +   +-----+-----+-----+-----+-----+----+
> > > +   |0x00 |0x01 |0x02 |0x03 |0x04 |0x05|
> > > +   | 1   | 2   |port |line | err | dir|
> > > +   +-----+-----+-----+-----+-----+----+
> > 
> > Sorry, but i don't see how two u8 vs six u8 are the same message format.
> > 
> 
> Some changes to the message format are necessary.
> 
> Virtio uses two communication channels (virtqueues): one for requests and replies, and a second one for events. 
> In contrast, rpmsg provides only a single communication channel, so a type field is required to distinguish between 
> different kinds of messages.
> 
> Since rpmsg replies and events share the same message format, an additional line is introduced to handle both cases.
> 
> Finally, rpmsg supports multiple GPIO controllers, so a port field is added to uniquely identify the target controller.

I have commented on this before - RPMSG is already providing multiplexing
capability by way of endpoints.  There is no need for a port field.  One
endpoint, one GPIO controller. 

> Shenwei
> >        Andrew