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

[Shenwei Wang]

> -----Original Message-----
> From: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Sent: Wednesday, April 29, 2026 10:42 AM
> To: Shenwei Wang <shenwei.wang@xxxxxxx>
> Cc: Andrew Lunn <andrew@xxxxxxx>; Padhi, Beleswar <b-padhi@xxxxxx>; Linus
> Walleij <linusw@xxxxxxxxxx>; Bartosz Golaszewski <brgl@xxxxxxxxxx>; Jonathan
> Corbet <corbet@xxxxxxx>; Rob Herring <robh@xxxxxxxxxx>; Krzysztof Kozlowski
> <krzk+dt@xxxxxxxxxx>; Conor Dooley <conor+dt@xxxxxxxxxx>; Bjorn Andersson
> <andersson@xxxxxxxxxx>; Frank Li <frank.li@xxxxxxx>; Sascha Hauer
> <s.hauer@xxxxxxxxxxxxxx>; Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>; linux-
> gpio@xxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx>; Fabio Estevam
> <festevam@xxxxxxxxx>; Peng Fan <peng.fan@xxxxxxx>;
> devicetree@xxxxxxxxxxxxxxx; linux-remoteproc@xxxxxxxxxxxxxxx;
> imx@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; dl-linux-imx <linux-
> imx@xxxxxxx>; Bartosz Golaszewski <brgl@xxxxxxxx>
> Subject: [EXT] Re: [PATCH v13 3/4] gpio: rpmsg: add generic rpmsg GPIO driver
> On Tue, Apr 28, 2026 at 03:24:59PM +0000, Shenwei Wang wrote:
> >
> >
> > > -----Original Message-----
> > > From: Andrew Lunn <andrew@xxxxxxx>
> > > Sent: Monday, April 27, 2026 3:49 PM
> > > To: Shenwei Wang <shenwei.wang@xxxxxxx>
> > > Cc: Padhi, Beleswar <b-padhi@xxxxxx>; Linus Walleij
> > > <linusw@xxxxxxxxxx>; Bartosz Golaszewski <brgl@xxxxxxxxxx>; Jonathan
> > > Corbet <corbet@xxxxxxx>; Rob Herring <robh@xxxxxxxxxx>; Krzysztof
> > > Kozlowski <krzk+dt@xxxxxxxxxx>; Conor Dooley <conor+dt@xxxxxxxxxx>;
> > > Bjorn Andersson <andersson@xxxxxxxxxx>; Mathieu Poirier
> > > <mathieu.poirier@xxxxxxxxxx>; Frank Li <frank.li@xxxxxxx>; Sascha
> > > Hauer <s.hauer@xxxxxxxxxxxxxx>; Shuah Khan
> > > <skhan@xxxxxxxxxxxxxxxxxxx>; linux-gpio@xxxxxxxxxxxxxxx; linux-
> > > doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Pengutronix
> > > Kernel Team <kernel@xxxxxxxxxxxxxx>; Fabio Estevam
> > > <festevam@xxxxxxxxx>; Peng Fan <peng.fan@xxxxxxx>;
> > > devicetree@xxxxxxxxxxxxxxx; linux- remoteproc@xxxxxxxxxxxxxxx;
> > > imx@xxxxxxxxxxxxxxx; linux-arm- kernel@xxxxxxxxxxxxxxxxxxx;
> > > dl-linux-imx <linux-imx@xxxxxxx>; Bartosz Golaszewski
> > > <brgl@xxxxxxxx>
> > > 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.
> 

You still need a way to let the remote side know which port the endpoint maps to, either 
by embedding the port information in the message (the current way), or by sending it 
separately.

Shenwei

> >
> > Shenwei
> >
> > >        Andrew