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From:   Sam Protsenko <semen.protsenko@linaro.org>
Date:   Mon, 29 Nov 2021 22:38:47 +0200
Message-ID: <CAPLW+4n+y2cARyeV53hBfUdbyy5ZtCCisDQ20ANF7mM0uh_V4g@mail.gmail.com>
Subject: Re: [PATCH 5/8] tty: serial: samsung: Enable console as module
To:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Cc:     Rob Herring <robh+dt@kernel.org>, Mark Brown <broonie@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jaewon Kim <jaewon02.kim@samsung.com>,
        Chanho Park <chanho61.park@samsung.com>,
        David Virag <virag.david003@gmail.com>,
        Youngmin Nam <youngmin.nam@samsung.com>,
        devicetree@vger.kernel.org, linux-spi@vger.kernel.org,
        linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
        linux-i2c@vger.kernel.org
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On Mon, 29 Nov 2021 at 22:18, Sam Protsenko <semen.protsenko@linaro.org> wrote:
>
> On Mon, 29 Nov 2021 at 10:52, Krzysztof Kozlowski
> <krzysztof.kozlowski@canonical.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@linaro.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.
>

...But I'll actually add proper error path handling in
samsung_serial_init(), i.e. unregister console if
platform_driver_register() fails. And I'll add the same console
unregister in samsung_serial_exit(), just in case.

> > > +
> > > +     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