Re: [PATCH v2 3/4] gpio: imx-rpmsg: add imx-rpmsg GPIO driver

[Shenwei Wang]

Hi Arnaud,

> -----Original Message-----
> From: Arnaud POULIQUEN <arnaud.pouliquen@xxxxxxxxxxx>
> Sent: Monday, October 6, 2025 4:53 AM
> To: Shenwei Wang <shenwei.wang@xxxxxxx>; Bjorn Andersson
> <andersson@xxxxxxxxxx>; Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>; Rob
> Herring <robh@xxxxxxxxxx>; Krzysztof Kozlowski <krzk+dt@xxxxxxxxxx>; Conor
> Dooley <conor+dt@xxxxxxxxxx>; Shawn Guo <shawnguo@xxxxxxxxxx>; Sascha
> Hauer <s.hauer@xxxxxxxxxxxxxx>; Linus Walleij <linus.walleij@xxxxxxxxxx>;
> Bartosz Golaszewski <brgl@xxxxxxxx>
> Cc: Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx>; Fabio Estevam
> <festevam@xxxxxxxxx>; Peng Fan <peng.fan@xxxxxxx>; linux-
> remoteproc@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx
> <linux-imx@xxxxxxx>; openamp-rp@xxxxxxxxxxxxxxxxxxxxxxxx
> Subject: [EXT] Re: [PATCH v2 3/4] gpio: imx-rpmsg: add imx-rpmsg GPIO driver
> >> Then, the RPMsg device should be probed either by the remote
> >> processor using the name service announcement mechanism or if not
> >> possible by your remoteproc driver.
> >>
> > The idea is to probe the GPIO driver successfully only after the remote
> processor is online and has sent the name service announcement.
> > Until then, the GPIO driver will remain in a deferred state, ensuring that all
> consumers of the associated GPIOs are also deferred.
> > The implementation you provided below does not guarantee that the
> > related consumers will be properly deferred. This is the most important
> behavior for a GPIO/I2C controllers.
> 
> 
> As long as you keep the GPIO/I2C device as a child of the remote processor node,
> you should not have deferred probe issues.
> The|of_platform_populate()|function ensures
> that the I2C/GPIO devices are probed when the remote processor is started.
> Calling|devm_gpiochip_add_data|in the RPMsg driver probe should also
> prevent such issues.
> 

Here, deferred probing is not an issue -it's an intentional feature. We need to ensure that all consumers of the GPIO/I2C controllers remain
in the deferred state until the remote processor is fully online.

For instance, consider a regulator node that references a GPIO line from the RPMSG GPIO controller. The regulator will stay in the deferred state 
until the remote processor comes online and its services are announced and received.

Thanks,
Shenwei

> Regards,
> Arnaud
> 
> >
> > Thanks,
> > Shenwei
> >
> >> To better understand my proposal you can have a look to [1]and [2].
> >> Here is another example for an rpmsg_i2c( ST downstream implementation):
> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit