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

[Shenwei Wang]

Hi Arnaud,

> -----Original Message-----
> From: Arnaud POULIQUEN <arnaud.pouliquen at foss.st.com>
> Sent: Monday, October 6, 2025 4:53 AM
> To: Shenwei Wang <shenwei.wang at nxp.com>; Bjorn Andersson
> <andersson at kernel.org>; Mathieu Poirier <mathieu.poirier at linaro.org>; Rob
> Herring <robh at kernel.org>; Krzysztof Kozlowski <krzk+dt at kernel.org>; Conor
> Dooley <conor+dt at kernel.org>; Shawn Guo <shawnguo at kernel.org>; Sascha
> Hauer <s.hauer at pengutronix.de>; Linus Walleij <linus.walleij at linaro.org>;
> Bartosz Golaszewski <brgl at bgdev.pl>
> Cc: Pengutronix Kernel Team <kernel at pengutronix.de>; Fabio Estevam
> <festevam at gmail.com>; Peng Fan <peng.fan at nxp.com>; linux-
> remoteproc at vger.kernel.org; devicetree at vger.kernel.org; imx at lists.linux.dev;
> linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org; dl-linux-imx
> <linux-imx at nxp.com>; openamp-rp at lists.openampproject.org
> 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