Re: [PATCH v8 3/4] gpio: rpmsg: add generic rpmsg GPIO driver

[Shenwei Wang]

> -----Original Message-----
> From: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Sent: Tuesday, February 24, 2026 4:47 PM
> To: Shenwei Wang <shenwei.wang@xxxxxxx>
> Cc: Andrew Lunn <andrew@xxxxxxx>; Arnaud POULIQUEN
> <arnaud.pouliquen@xxxxxxxxxxx>; 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 v8 3/4] gpio: rpmsg: add generic rpmsg GPIO driver
> > > -----Original Message-----
> > > From: Andrew Lunn <andrew@xxxxxxx>
> > > Sent: Tuesday, February 24, 2026 4:23 PM
> > > To: Shenwei Wang <shenwei.wang@xxxxxxx>
> > > Cc: Arnaud POULIQUEN <arnaud.pouliquen@xxxxxxxxxxx>; 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: Re: [EXT] Re: [PATCH v8 3/4] gpio: rpmsg: add generic rpmsg
> > > GPIO driver
> > >
> > > Caution: This is an external email. Please take care when clicking
> > > links or opening attachments. When in doubt, report the message using the
> 'Report this email'
> > > button
> > >
> > >
> > > > > > + remote_cm33{
> > > > > > +     rpmsg {
> > > > > > +        rpmsg-io-channel {
> > > > > > +          #address-cells = <1>;
> > > > > > +          #size-cells = <0>;
> > > > > > +
> > > > > > +          gpio@0 {
> > > > > > +            compatible = "rpmsg-gpio";
> > > > > > +            reg = <0>;
> > > > > > +            gpio-controller;
> > > > > > +            #gpio-cells = <2>;
> > > > > > +            #interrupt-cells = <2>;
> > > > > > +            interrupt-controller;
> > > > > > +          };
> > > > > > +          gpio@1 {
> > > > > > +            compatible = "rpmsg-gpio";
> > > > > > +            reg = <1>;
> > > > > > +            gpio-controller;
> > > > > > +            #gpio-cells = <2>;
> > > > > > +            #interrupt-cells = <2>;
> > > > > > +            interrupt-controller;
> > > > > > +          };
> > >
> > > > Then how would you distinguish gpio@0 from gpio@1 on the CM33
> > > > RPMSG bus
> > > in the example above?
> > > > They are running on the same transport.
> > >
> > > Doesn't reg indicate the channel number? gpio@0 is on rpmsg channel
> > > 0. gpio@1 is on channel 1? The reg value gets filled into struct
> > > rpmsg_channel_info when the endpoints are created?
> >
> > There is only a single RPMSG channel for the CM33 remoteproc in this
> > example-its name is "rpmsg-io-channel". As I mentioned above, both gpio@0
> and gpio@1 run over this same transport.
> > The transport here is the RPMSG channel, so multiple GPIO controllers share
> that channel.
> >
> 
> That is one of my main problem with this proposal - multiplexing several GPIO
> controllers over the same RPMSG channel adds complexity.

Multiplexing multiple GPIO controllers over a single RPMSG channel does not inherently 
add complexity. Even if we implement a “one GPIO controller per RPMSG channel” model, 
the core logic in the driver remains essentially the same.

In fact, the current implementation already supports your preferred “one RPMSG channel 
per GPIO controller” approach through simple DTS configuration. For example:

+ remote_cm33{
+     rpmsg {
+        channel0 {    
+          gpio@0 {
+            compatible = "rpmsg-gpio";
+            reg = <0>;
+            gpio-controller;
+            #gpio-cells = <2>;
+            #interrupt-cells = <2>;
+            interrupt-controller;
+          };
+       };
+
+        channel1 {
+          gpio@1 {
+            compatible = "rpmsg-gpio";
+            reg = <1>;
+            gpio-controller;
+            #gpio-cells = <2>;
+            #interrupt-cells = <2>;
+            interrupt-controller;
+          };
+        };
+      };
+};
+

> RPMSG can already handle multiplexing via channels, use one RPMSG channel
> per GPIO controller.
> 
> > Thanks,
> > Shenwei
> >
> > >
> > >    Andrew
> >