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

[Padhi, Beleswar]

Hi Mathieu,

On 4/29/2026 11:03 PM, Mathieu Poirier wrote:
> On Wed, 29 Apr 2026 at 10:53, Shenwei Wang <shenwei.wang@xxxxxxx> wrote:
> > > -----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.
> An endpoint is created with every namespace request.  There should be
> one namespace request for every GPIO controller, which yields a unique
> endpoint for each controller and eliminates the need for an extra
> field to identify them.


Right, but this can still be done by just having one namespace request.
We can create new endpoints bound to an existing namespace/channel by
invoking rpmsg_create_ept(). This is what I suggested here too:
https://lore.kernel.org/all/29485742-6e49-482e-b73d-228295daaeec@xxxxxx/

My mental model looks like this for the complete picture:

1. namespace/channel#1 = rpmsg-io
   a. ept1 -> gpio-controller@1
   b. ept2 -> gpio-controller@2

2. namespace/channel#2 = rpmsg-i2c
   a. ept1 -> i2c@1
   b. ept2 -> i2c@2
   c. ept3 -> i2c@3

etc...

This way device groups are isolated with each channel/namespace, and
instances within each device groups are also respected with specific
endpoints.

Thanks,
Beleswar