linux-kernel - Re: [PATCH v1 2/5] tty: serial: meson: redesign the module to platform

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Date:   Tue, 4 Jul 2023 16:46:40 +0200
From:   neil.armstrong@...aro.org
To:     Dmitry Rokosov <ddrokosov@...rdevices.ru>,
        gregkh@...uxfoundation.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        jbrunet@...libre.com, jirislaby@...nel.org, khilman@...libre.com,
        martin.blumenstingl@...glemail.com
Cc:     kelvin.zhang@...ogic.com, xianwei.zhao@...ogic.com,
        kernel@...rdevices.ru, rockosov@...il.com,
        linux-amlogic@...ts.infradead.org, linux-serial@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 2/5] tty: serial: meson: redesign the module to
 platform_driver

On 04/07/2023 15:59, Dmitry Rokosov wrote:
> Actually, the meson_uart module is already a platform_driver, but it is
> currently registered manually and the uart core registration is run
> outside the probe() scope, which results in some restrictions. For
> instance, it is not possible to communicate with the OF subsystem
> because it requires an initialized device object.
> 
> To address this issue, apply module_platform_driver() instead of direct
> module init/exit routines. Additionally, move uart_register_driver() to
> the driver probe(), and destroy manual console registration because it's
> already run in the uart_register_driver() flow.
> 
> Signed-off-by: Dmitry Rokosov <ddrokosov@...rdevices.ru>
> ---
>   drivers/tty/serial/meson_uart.c | 46 +++++++--------------------------
>   1 file changed, 10 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> index 169f028956ae..87c0eb5f2dba 100644
> --- a/drivers/tty/serial/meson_uart.c
> +++ b/drivers/tty/serial/meson_uart.c
> @@ -621,12 +621,6 @@ static struct console meson_serial_console = {
>   	.data		= &meson_uart_driver,
>   };
>   
> -static int __init meson_serial_console_init(void)
> -{
> -	register_console(&meson_serial_console);
> -	return 0;
> -}
> -
>   static void meson_serial_early_console_write(struct console *co,
>   					     const char *s,
>   					     u_int count)
> @@ -652,9 +646,6 @@ OF_EARLYCON_DECLARE(meson, "amlogic,meson-ao-uart",
>   
>   #define MESON_SERIAL_CONSOLE	(&meson_serial_console)
>   #else
> -static int __init meson_serial_console_init(void) {
> -	return 0;
> -}
>   #define MESON_SERIAL_CONSOLE	NULL
>   #endif
>   
> @@ -738,6 +729,13 @@ static int meson_uart_probe(struct platform_device *pdev)
>   	if (ret)
>   		return ret;
>   
> +	if (!meson_uart_driver.state) {
> +		ret = uart_register_driver(&meson_uart_driver);
> +		if (ret)
> +			return dev_err_probe(&pdev->dev, ret,
> +				      "failed to register meson-uart driver\n");
> +	}

PL010 protects this in a mutex, and I think you should do the same otherwise
if multiple uart probes at the same it will do weird stuff.

> +
>   	port->iotype = UPIO_MEM;
>   	port->mapbase = res_mem->start;
>   	port->mapsize = resource_size(res_mem);
> @@ -776,6 +774,8 @@ static int meson_uart_remove(struct platform_device *pdev)
>   	uart_remove_one_port(&meson_uart_driver, port);
>   	meson_ports[pdev->id] = NULL;
>   
> +	uart_unregister_driver(&meson_uart_driver);
> +

This is dangerous, it will remove the driver even if some uart are still attached to it.

You should probably do like in pl010_remove() and remove only if the last one is removed.

>   	return 0;
>   }
>   
> @@ -809,33 +809,7 @@ static  struct platform_driver meson_uart_platform_driver = {
>   	},
>   };
>   
> -static int __init meson_uart_init(void)
> -{
> -	int ret;
> -
> -	ret = meson_serial_console_init();
> -	if (ret)
> -		return ret;
> -	
> -	ret = uart_register_driver(&meson_uart_driver);
> -	if (ret)
> -		return ret;
> -
> -	ret = platform_driver_register(&meson_uart_platform_driver);
> -	if (ret)
> -		uart_unregister_driver(&meson_uart_driver);
> -
> -	return ret;
> -}
> -
> -static void __exit meson_uart_exit(void)
> -{
> -	platform_driver_unregister(&meson_uart_platform_driver);
> -	uart_unregister_driver(&meson_uart_driver);
> -}
> -
> -module_init(meson_uart_init);
> -module_exit(meson_uart_exit);
> +module_platform_driver(meson_uart_platform_driver);

Only pl010 uses this scheme, and I don't know why... if it works then it's ok for me.

Thanks,
Neil

>   
>   MODULE_AUTHOR("Carlo Caione <carlo@...one.org>");
>   MODULE_DESCRIPTION("Amlogic Meson serial port driver");