RE: [PATCH V2 1/4] gpio: mxc: Support module build

[Anson Huang]

Hi, Linus
	Do you have chance to take a look at this patch series?

Thanks,
Anson


> Subject: Re: [PATCH V2 1/4] gpio: mxc: Support module build
> 
> On Mon, Jul 27, 2020 at 2:23 PM Anson Huang <anson.huang@xxxxxxx>
> wrote:
> > > Subject: Re: [PATCH V2 1/4] gpio: mxc: Support module build
> > >
> > > > So, could you please help advise how to proceed it for this GPIO
> > > > driver to  support loadable module?
> > >
> > > I would start by getting a reference board to work with a kernel in
> > > which all drivers are built-in except for the pinctrl driver, to see
> > > what exactly breaks when you do that, and what other drivers may have
> the same problems.
> > > Maybe it's not that bad after all and you only need a few modifications.
> > >
> >
> > I agreed, but the situation is i.MX SoC contains more than 20 modules,
> > and most of them are NOT owned by me, so I am NOT sure when the module
> > owner will start working on the support. And if with minimum devices
> > enabled, such as tiny kernel with ramfs, it is working even with pinctrl/clock
> etc. built as loadable module.
> 
> Do you have an example that is actually broken? I checked how the gpio chip
> is actually used and found that "regulator-fixed", "virtual,mdio-gpio",
> "regulator-gpio", "gpio-leds", "marvell,mv88e6085", "microchip,usb2513b",
> "fsl,imx7d-usdhc", "fsl,imx6sx-fec", "mmc-pwrseq-simple",
> "brcm,bcm43438-bt",  "rohm,bd71837", "nxp,pca9546",  "rtc-m41t80",
> should all work fine here.
> 
> I'm not sure about "fsl,mma8451", maybe test that one manually or look at
> the driver in more detail.
> 
> "fsl,imx8mq-pcie" looks broken but easily fixed, and this is something we have
> already discussed.
> 
> imx8mq-nitrogen.c has a "vsel-gpios" property in its "fcs,fan53555"
> device node that is neither part of the binding nor handled by the driver, so
> this is broken regardless of the gpio driver.
> 
> > Meanwhile, as you said, most of the users are still using built-in
> > model, so adding the support for GPIO can be in parallel with other
> > modules' work, in other words, with this GPIO loadable module support
> > patch, if other modules can NOT work due to lack of defer probe
> > implementation, then the patch should be done in other module, adding
> > that the default configuration of GPIO is still built-in, do you think it can be
> an independent patch and get into linux-next first?
> 
> I think you should be reasonably sure that making the driver a loadable
> module does not break other drivers that might rely on the probe order and
> that are known to be used with an i.MX chip. With the list above, that seems
> to actually be the case for the most part, but testing is always better.
> 
> If there are boards that use other drivers which do not support deferred
> probing but don't have those listed in the dts files in the kernel, then that is
> not something you have to worry about I think.
> 
> I'll let Linus Walleij comment on whether he thinks the initcall should stay at
> subsys_initcall() to avoid breaking users with buggy drivers, or whether this
> should be changed to module_init() or builtin_platform_driver() to have a
> better chance of finding and fixing those broken drivers.
> 
>      Arnd