linux-kernel - RE: [PATCH V4 5/5] clk: imx8qxp: Support building i.MX8QXP clock driver as module

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Date:   Thu, 2 Jul 2020 05:50:46 +0000
From:   Anson Huang <anson.huang@....com>
To:     Dong Aisheng <dongas86@...il.com>, Arnd Bergmann <arnd@...db.de>
CC:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Peng Fan <peng.fan@....com>, Abel Vesa <abel.vesa@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        Andy Duan <fugang.duan@....com>,
        Daniel Baluta <daniel.baluta@....com>,
        YueHaibing <yuehaibing@...wei.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-clk <linux-clk@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V4 5/5] clk: imx8qxp: Support building i.MX8QXP clock
 driver as module



> Subject: Re: [PATCH V4 5/5] clk: imx8qxp: Support building i.MX8QXP clock
> driver as module
> 
> On Thu, Jul 2, 2020 at 11:55 AM Anson Huang <anson.huang@....com>
> wrote:
> [...]
> > > > +{
> > > > +       return platform_driver_register(&imx8qxp_lpcg_clk_driver);
> > > > +}
> > > > +device_initcall(imx8qxp_lpcg_clk_init);
> > >
> > > Any reason to change to device_initcall which looks a bit strange?
> > > Is it because the following line?
> > > +obj-$(CONFIG_MXC_CLK_SCU) += clk-imx-scu.o clk-imx-lpcg-scu.o
> > > But it looks to me they're still two modules. Aren't they?
> >
> > It is suggested by Arnd to NOT use builtin_platform_driver(), in order
> > to support module unload, although the clock driver normally does NOT
> > support remove, but it is better to follow the right way.
> >
> 
> By expanding builtin_platform_driver() marcro, you will find your patch is
> exactly doing the same thing as buildin_platform_driver() which obivously is
> unneccesary.
> 
> #define builtin_platform_driver(__platform_driver) \
>         builtin_driver(__platform_driver, platform_driver_register) #define
> builtin_driver(__driver, __register, ...) \
> 
> static int __init __driver##_init(void) \ { \
>         return __register(&(__driver) , ##__VA_ARGS__); \ } \
> device_initcall(__driver##_init);
> 
> If we want to support unload, we need a .remove() callback as current clocks
> are not allocated by devm_().
> If don't support,  we probably can use builtin_platform_driver() first and
> switch to module_platform_driver() in the future once the driver supports
> release resource properly.
> 

Yes, that is why I use the device_initcall() to make it exactly same as builtin_driver(),
and also yes that i.MX clock driver does NOT support module unload, so .remove()
is NOT implemented, I am fine with either way, just try to address Arnd's comment.

Hi, Arnd
	What do you think? Do you agree to keep using the builtin_driver()?

Thanks,
Anson