linux-kernel - Re: [PATCH v4 4/4] serial: core: Add serial_base_match_and_update_preferred

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Date: Fri, 21 Jun 2024 14:37:27 +0200
From: Petr Mladek <pmladek@...e.com>
To: Tony Lindgren <tony.lindgren@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tony Lindgren <tony@...mide.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/4] serial: core: Add
 serial_base_match_and_update_preferred_console()

On Thu 2024-06-20 15:45:29, Tony Lindgren wrote:
> Let's add serial_base_match_and_update_preferred_console() for consoles
> using DEVNAME:0.0 style naming.
> 
> The earlier approach to add it caused issues in the kernel command line
> ordering as we were calling __add_preferred_console() again for the
> deferred consoles.
> 
> Signed-off-by: Tony Lindgren <tony.lindgren@...ux.intel.com>

Looks good and seems to work well:

Reviewed-by: Petr Mladek <pmladek@...e.com>
Tested-by: Petr Mladek <pmladek@...e.com>

See an idea below.

> --- a/drivers/tty/serial/serial_base_bus.c
> +++ b/drivers/tty/serial/serial_base_bus.c
> @@ -204,6 +205,42 @@ void serial_base_port_device_remove(struct serial_port_device *port_dev)
>  	put_device(&port_dev->dev);
>  }
>  
> +#ifdef CONFIG_SERIAL_CORE_CONSOLE
> +
> +/**
> + * serial_base_match_and_update_preferred_console - Match and update a preferred console
> + * @drv: Serial port device driver
> + * @port: Serial port instance
> + *
> + * Tries to match and update the preferred console for a serial port for
> + * the kernel command line option console=DEVNAME:0.0.
> + *
> + * Cannot be called early for ISA ports, depends on struct device.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +int serial_base_match_and_update_preferred_console(struct uart_driver *drv,
> +						   struct uart_port *port)
> +{
> +	const char *port_match __free(kfree) = NULL;
> +	int ret;
> +
> +	port_match = kasprintf(GFP_KERNEL, "%s:%d.%d", dev_name(port->dev),
> +			       port->ctrl_id, port->port_id);
> +	if (!port_match)
> +		return -ENOMEM;

The name is going to be compared with:

struct console_cmdline
{
[...]
	char	devname[32];			/* DEVNAME:0.0 style device name */

It looks like an overkill to allocate such a small buffer. It would
be perfectly fine to use a buffer on stack.

Well, we would need to define somewhere (likely in include/linux/console.h):

#define CONSOLE_DEVNAME_LEN 32

and then do

	char port_match[CONSOLE_DEVNAME_LEN];
	int len;

	len = snprintf(port_match, ARRAY_SIZE(port_match), "%s:%d.%d",
		       dev_name(port->dev), port->ctrl_id, port->port_id);
	if (len >= ARRAY_SIZE(port_match)) {
		pr_warn("Console devname does not fit into the buffer: "%s:%d.%d\n",
			 dev_name(port->dev), port->ctrl_id, port->port_id);
		return -ENOMEM;
	}

The advantage is that it would warn when there are longer device names.
It would help to catch situations when CONSOLE_DEVNAME_LEN is not big enough.

It might be done in a separate patch.

> +
> +	ret = match_devname_and_update_preferred_console(port_match,
> +							 drv->dev_name,
> +							 port->line);
> +	if (ret == -ENOENT)
> +		return 0;
> +
> +	return ret;
> +}
> +
> +#endif
> +
>  static int serial_base_init(void)
>  {
>  	int ret;

Best Regards,
Petr