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

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Tue, Apr 28, 2026 at 03:24:59PM +0000, Shenwei Wang wrote:
> 
> 
> > -----Original Message-----
> > From: Andrew Lunn <andrew@lunn.ch>
> > Sent: Monday, April 27, 2026 3:49 PM
> > To: Shenwei Wang <shenwei.wang@nxp.com>
> > Cc: Padhi, Beleswar <b-padhi@ti.com>; Linus Walleij <linusw@kernel.org>;
> > Bartosz Golaszewski <brgl@kernel.org>; Jonathan Corbet <corbet@lwn.net>;
> > Rob Herring <robh@kernel.org>; Krzysztof Kozlowski <krzk+dt@kernel.org>;
> > Conor Dooley <conor+dt@kernel.org>; Bjorn Andersson
> > <andersson@kernel.org>; Mathieu Poirier <mathieu.poirier@linaro.org>; Frank Li
> > <frank.li@nxp.com>; Sascha Hauer <s.hauer@pengutronix.de>; Shuah Khan
> > <skhan@linuxfoundation.org>; linux-gpio@vger.kernel.org; linux-
> > doc@vger.kernel.org; linux-kernel@vger.kernel.org; Pengutronix Kernel Team
> > <kernel@pengutronix.de>; Fabio Estevam <festevam@gmail.com>; Peng Fan
> > <peng.fan@nxp.com>; devicetree@vger.kernel.org; linux-
> > remoteproc@vger.kernel.org; imx@lists.linux.dev; linux-arm-
> > kernel@lists.infradead.org; dl-linux-imx <linux-imx@nxp.com>; Bartosz
> > Golaszewski <brgl@bgdev.pl>
> > 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