linux-kernel - Re: [PATCH 5/8] tty: serial: samsung: Enable console as module

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Message-ID: <CAPLW+4=Xp0m3ycm5c1WSJGtr6vRxx1fsW0MOo65fXMfaB1sR+w@mail.gmail.com>
Date:   Mon, 29 Nov 2021 22:18:31 +0200
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jaewon Kim <jaewon02.kim@...sung.com>,
        Chanho Park <chanho61.park@...sung.com>,
        David Virag <virag.david003@...il.com>,
        Youngmin Nam <youngmin.nam@...sung.com>,
        devicetree@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH 5/8] tty: serial: samsung: Enable console as module

On Mon, 29 Nov 2021 at 10:52, Krzysztof Kozlowski
<krzysztof.kozlowski@...onical.com> wrote:
>
> On 27/11/2021 23:32, Sam Protsenko wrote:
> > Enable serial driver to be built as a module. To do so, init the console
> > support on driver/module load instead of using console_initcall().
> >
> > This is needed for proper support of USIv2 driver (which can be built as
> > a module, which in turn makes SERIAL_SAMSUNG be a module too). It also
> > might be useful for Android GKI modularization efforts.
> >
> > Inspired by commit 87a0b9f98ac5 ("tty: serial: meson: enable console as
> > module").
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> > ---
> >  drivers/tty/serial/Kconfig       |  2 +-
> >  drivers/tty/serial/samsung_tty.c | 21 +++++++++++++++++++--
> >  2 files changed, 20 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> > index fc543ac97c13..0e5ccb25bdb1 100644
> > --- a/drivers/tty/serial/Kconfig
> > +++ b/drivers/tty/serial/Kconfig
> > @@ -263,7 +263,7 @@ config SERIAL_SAMSUNG_UARTS
> >
> >  config SERIAL_SAMSUNG_CONSOLE
> >       bool "Support for console on Samsung SoC serial port"
> > -     depends on SERIAL_SAMSUNG=y
> > +     depends on SERIAL_SAMSUNG
> >       select SERIAL_CORE_CONSOLE
> >       select SERIAL_EARLYCON
> >       help
> > diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> > index f986a9253dc8..92a63e9392ed 100644
> > --- a/drivers/tty/serial/samsung_tty.c
> > +++ b/drivers/tty/serial/samsung_tty.c
> > @@ -1720,10 +1720,10 @@ static int __init s3c24xx_serial_console_init(void)
> >       register_console(&s3c24xx_serial_console);
> >       return 0;
> >  }
> > -console_initcall(s3c24xx_serial_console_init);
> >
> >  #define S3C24XX_SERIAL_CONSOLE &s3c24xx_serial_console
> >  #else
> > +static inline int s3c24xx_serial_console_init(void) { return 0; }
> >  #define S3C24XX_SERIAL_CONSOLE NULL
> >  #endif
> >
> > @@ -2898,7 +2898,24 @@ static struct platform_driver samsung_serial_driver = {
> >       },
> >  };
> >
> > -module_platform_driver(samsung_serial_driver);
> > +static int __init samsung_serial_init(void)
> > +{
> > +     int ret;
> > +
> > +     ret = s3c24xx_serial_console_init();
> > +     if (ret)
> > +             return ret;
>
> This will trigger warns on module re-loading, won't it? Either suppress
> unbind or cleanup in module exit.
>

I guess that's already taken care of in  samsung_serial_remove(): it's
doing uart_remove_one_port(), which in turn does unregister_console().
So I don't think anything extra should be done on module exit. Or I'm
missing something?

That case (unload/load) actually doesn't work well in my case: serial
console doesn't work after doing "modprobe -r samsung_tty; modprobe
samsung_tty" (but it works fine e.g. in case of i2c_exynos5 driver).
Not sure what is wrong, but I can see that my board keeps running
(heartbeat LED is still blinking). Not even sure if that use case
(unload/load) was ever functional before.

Anyway, please let me know if you think something should be done about
this particular patch. Right now I don't see anything missing.

> > +
> > +     return platform_driver_register(&samsung_serial_driver);
> > +}
> > +
> > +static void __exit samsung_serial_exit(void)
> > +{
> > +     platform_driver_unregister(&samsung_serial_driver);
> > +}
> > +
> > +module_init(samsung_serial_init);
> > +module_exit(samsung_serial_exit);
> >
> >  #ifdef CONFIG_SERIAL_SAMSUNG_CONSOLE
> >  /*
> >
>
>
> Best regards,
> Krzysztof