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

[Shenwei Wang]

> -----Original Message-----
> From: Mathieu Poirier <mathieu.poirier at linaro.org>
> Sent: Tuesday, February 24, 2026 4:47 PM
> To: Shenwei Wang <shenwei.wang at nxp.com>
> Cc: Andrew Lunn <andrew at lunn.ch>; Arnaud POULIQUEN
> <arnaud.pouliquen at foss.st.com>; Linus Walleij <linusw at kernel.org>; Bartosz
> Golaszewski <brgl at kernel.org>; Jonathan Corbet <corbet at lwn.net>; Rob Herring
> <robh at kernel.org>; Krzysztof Kozlowski <krzk+dt at kernel.org>; Conor Dooley
> <conor+dt at kernel.org>; Bjorn Andersson <andersson at kernel.org>; Frank Li
> <frank.li at nxp.com>; Sascha Hauer <s.hauer at pengutronix.de>; Shuah Khan
> <skhan at linuxfoundation.org>; linux-gpio at vger.kernel.org; linux-
> doc at vger.kernel.org; linux-kernel at vger.kernel.org; Pengutronix Kernel Team
> <kernel at pengutronix.de>; Fabio Estevam <festevam at gmail.com>; Peng Fan
> <peng.fan at nxp.com>; devicetree at vger.kernel.org; linux-
> remoteproc at vger.kernel.org; imx at lists.linux.dev; linux-arm-
> kernel at lists.infradead.org; dl-linux-imx <linux-imx at nxp.com>; Bartosz
> Golaszewski <brgl at bgdev.pl>
> Subject: [EXT] Re: [PATCH v8 3/4] gpio: rpmsg: add generic rpmsg GPIO driver
> > > -----Original Message-----
> > > From: Andrew Lunn <andrew at lunn.ch>
> > > Sent: Tuesday, February 24, 2026 4:23 PM
> > > To: Shenwei Wang <shenwei.wang at nxp.com>
> > > Cc: Arnaud POULIQUEN <arnaud.pouliquen at foss.st.com>; Linus Walleij
> > > <linusw at kernel.org>; Bartosz Golaszewski <brgl at kernel.org>; Jonathan
> > > Corbet <corbet at lwn.net>; Rob Herring <robh at kernel.org>; Krzysztof
> > > Kozlowski <krzk+dt at kernel.org>; Conor Dooley <conor+dt at kernel.org>;
> > > Bjorn Andersson <andersson at kernel.org>; Mathieu Poirier
> > > <mathieu.poirier at linaro.org>; Frank Li <frank.li at nxp.com>; Sascha
> > > Hauer <s.hauer at pengutronix.de>; Shuah Khan
> > > <skhan at linuxfoundation.org>; linux-gpio at vger.kernel.org; linux-
> > > doc at vger.kernel.org; linux-kernel at vger.kernel.org; Pengutronix
> > > Kernel Team <kernel at pengutronix.de>; Fabio Estevam
> > > <festevam at gmail.com>; Peng Fan <peng.fan at nxp.com>;
> > > devicetree at vger.kernel.org; linux- remoteproc at vger.kernel.org;
> > > imx at lists.linux.dev; linux-arm- kernel at lists.infradead.org;
> > > dl-linux-imx <linux-imx at nxp.com>; Bartosz Golaszewski
> > > <brgl at bgdev.pl>
> > > 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 at 0 {
> > > > > > +            compatible = "rpmsg-gpio";
> > > > > > +            reg = <0>;
> > > > > > +            gpio-controller;
> > > > > > +            #gpio-cells = <2>;
> > > > > > +            #interrupt-cells = <2>;
> > > > > > +            interrupt-controller;
> > > > > > +          };
> > > > > > +          gpio at 1 {
> > > > > > +            compatible = "rpmsg-gpio";
> > > > > > +            reg = <1>;
> > > > > > +            gpio-controller;
> > > > > > +            #gpio-cells = <2>;
> > > > > > +            #interrupt-cells = <2>;
> > > > > > +            interrupt-controller;
> > > > > > +          };
> > >
> > > > Then how would you distinguish gpio at 0 from gpio at 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 at 0 is on rpmsg channel
> > > 0. gpio at 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 at 0
> and gpio at 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 at 0 {
+            compatible = "rpmsg-gpio";
+            reg = <0>;
+            gpio-controller;
+            #gpio-cells = <2>;
+            #interrupt-cells = <2>;
+            interrupt-controller;
+          };
+       };
+
+        channel1 {
+          gpio at 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
> >