Re: [PATCH v5 0/5] Enable Remote GPIO over RPMSG on i.MX Platform

Shenwei Wang
2025-11-07T22:40:34Z

> -----Original Message-----
> From: Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>
> Sent: Friday, November 7, 2025 11:18 AM
> To: Shenwei Wang <shenwei.wang@nxp.com>; Peng Fan <peng.fan@nxp.com>;
> Bjorn Andersson <andersson@kernel.org>; Mathieu Poirier
> <mathieu.poirier@linaro.org>; Rob Herring <robh@kernel.org>; Krzysztof
> Kozlowski <krzk+dt@kernel.org>; Conor Dooley <conor+dt@kernel.org>; Shawn
> Guo <shawnguo@kernel.org>; Sascha Hauer <s.hauer@pengutronix.de>;
> Jonathan Corbet <corbet@lwn.net>; Linus Walleij <linus.walleij@linaro.org>;
> Bartosz Golaszewski <brgl@bgdev.pl>
> Cc: Pengutronix Kernel Team <kernel@pengutronix.de>; Fabio Estevam
> <festevam@gmail.com>; linux-remoteproc@vger.kernel.org;
> devicetree@vger.kernel.org; imx@lists.linux.dev; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> doc@vger.kernel.org; dl-linux-imx <linux-imx@nxp.com>; Randy Dunlap
> <rdunlap@infradead.org>; Andrew Lunn <andrew@lunn.ch>; linux-
> gpio@vger.kernel.org
> Subject: [EXT] Re: [PATCH v5 0/5] Enable Remote GPIO over RPMSG on i.MX
> Platform
> >>>>> I have not look into the details of new version, but before that,
> >>>>> just want to check, have we agreed on what Arnaud suggested?
> >>>>> or continue to proceed to be this as i.MX specific?
> >>>>
> >>>> Thanks, Peng, for pointing this out. Regarding the V3 discussions,
> >>>> it seems that I am not the only one suggesting a generic driver.
> >>>>
> >>>
> >>> As I mentioned before, the only i.MX-specific part is the transport
> >>> protocol over
> >> the RPMSG bus.
> >>> In this v5 patches, we've included detailed documentation for the
> >>> protocol in a separate file. Any platform that follows the same
> >>> protocol should
> >> work right out of the box.
> >>>
> >>> If you spot anything that could be improved, please let me know!
> >>
> >> My concerns remain the same as those shared previously:
> >>
> >> 1) The simpler one: gpio-imx-rpmsg.c should be renamed to gpio-rpmsg.c.
> >>
> >
> > Agree. Will fix it in the next version.
> >
> >> 2) The more complex one: the driver should be independent of the
> >> remoteproc driver. The rpmsg protocol relies on virtio and can be
> >> used in contexts other than remoteproc. In other words, the struct
> >> rpmsg_driver and its associated operations should be defined within
> >> the rpmsg-gpio driver, not in the remoteproc driver.
> >>
> >
> > The GPIO driver operates independently of the remoteproc driver.
>
> The channel_device_map table in imx_rproc.c would give me the opposite feeling
>
> It functions based

The channel_device_map is used to control the order in which devices are populated.
This mechanism is key to implementing the probe-defer feature for the GPIO driver.
For those who don't care about the probe DEFER, you don't need to put the devices in the map.

> > on the defined GPIO-RPMSG transport protocol. Any remoteproc that
> > supports this protocol can exchange data with the GPIO driver via the
> underlying rpmsg bus.
> > Placing the rpmsg_driver (which manages the rpmsg channel) within the
> > remoteproc driver is more logical, as rpmsg channels run on the rpmsg
> > bus. This bus is defined inside the remoteproc device tree node and is
> populated by the corresponding remoteproc driver.
>
>
> Regarding imx_of_rpmsg_node_init(), It seems you rely on device tree in the
> rproc platform to register rpmsg drivers. This implies you are creating drivers
> based on a device description. To me, this does not appear to be a valid
> implementation, but perhaps such an approach already exists in the Linux kernel?
>

This follows a standard DTS population approach. Regardless of how the code is organized,
you need the logic somewhere to populate the devices. Placing the "rpmsg" bus under the
remoteproc node is more straightforward because the bus depends on the remote processor.

>
> For your information, I'm facing a similar issue with my remoteproc_tee series
> [1]. The advice I received was to look at the PCIe DT implementation (I haven't
> had time to explore it yet). This advice also seems relevant to your series.
>
> Do you also have a look to rpmsg_virtio_bus ? it seems a good candidate to
> match the device tree properties with the rpmsg device?
>

The implementation is actually based on the rpmsg_virtio_bus. The rpmsg_send
Will finally call virtio_rpmsg_send.

Thanks,
Shenwei

> In the end, this is my point of view. Perhaps it is better to wait for others before
> deciding on the direction...
>
> Thanks,
> Arnaud
>
> [1]https://lists.infr/
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> October%2F1069154.html&data=05%7C02%7Cshenwei.wang%40nxp.com%7C0
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>
> >
> > Thanks,
> > Shenwei
> >
> >>
> >> Thanks,
> >> Arnaud
> >>
> >>>
> >>> Thanks,
> >>> Shenwei
> >>>
> >>>> Thanks,
> >>>> Arnaud
> >>>>
> >>>>>
> >>>>> Thanks
> >>>>> Peng.
> >>>
> >