linux-kernel - Re: [PATCH] serial: earlycon: prefer EARLYCON

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Date:   Fri, 28 Feb 2020 11:26:36 +0100
From:   Michael Walle <michael@...le.cc>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: earlycon: prefer EARLYCON_DECLARE() variant

Hi Greg,


Am 2020-02-20 18:46, schrieb Michael Walle:
> If a driver exposes early consoles with EARLYCON_DECLARE() and
> OF_EARLYCON_DECLARE(), pefer the non-OF variant if the user specifies 
> it
> by
>   earlycon=<driver>,<options>
> 
> The rationale behind this is that some drivers register multiple setup
> functions under the same driver name. Eg.
> 
> OF_EARLYCON_DECLARE(lpuart, "fsl,vf610-lpuart", 
> lpuart_early_console_setup);
> OF_EARLYCON_DECLARE(lpuart32, "fsl,ls1021a-lpuart",
> lpuart32_early_console_setup);
> OF_EARLYCON_DECLARE(lpuart32, "fsl,imx7ulp-lpuart",
> lpuart32_imx_early_console_setup);
> EARLYCON_DECLARE(lpuart, lpuart_early_console_setup);
> EARLYCON_DECLARE(lpuart32, lpuart32_early_console_setup);
> 
> It depends on the order of the entries which console_setup() actually
> gets called. To make things worse, I guess it also depends on the
> compiler how these are ordered. Thus always prefer the 
> EARLYCON_DECLARE()
> ones.

Do you have an opinon on this proposal?

-michael

> 
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
>  drivers/tty/serial/earlycon.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/tty/serial/earlycon.c 
> b/drivers/tty/serial/earlycon.c
> index c14873b67803..2ae9190b64bb 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -170,6 +170,7 @@ static int __init register_earlycon(char *buf,
> const struct earlycon_id *match)
>  int __init setup_earlycon(char *buf)
>  {
>  	const struct earlycon_id **p_match;
> +	bool empty_compatible = true;
> 
>  	if (!buf || !buf[0])
>  		return -EINVAL;
> @@ -177,6 +178,7 @@ int __init setup_earlycon(char *buf)
>  	if (early_con.flags & CON_ENABLED)
>  		return -EALREADY;
> 
> +again:
>  	for (p_match = __earlycon_table; p_match < __earlycon_table_end;
>  	     p_match++) {
>  		const struct earlycon_id *match = *p_match;
> @@ -185,6 +187,10 @@ int __init setup_earlycon(char *buf)
>  		if (strncmp(buf, match->name, len))
>  			continue;
> 
> +		/* prefer entries with empty compatible */
> +		if (empty_compatible && *match->compatible)
> +			continue;
> +
>  		if (buf[len]) {
>  			if (buf[len] != ',')
>  				continue;
> @@ -195,6 +201,11 @@ int __init setup_earlycon(char *buf)
>  		return register_earlycon(buf, match);
>  	}
> 
> +	if (empty_compatible) {
> +		empty_compatible = false;
> +		goto again;
> +	}
> +
>  	return -ENOENT;
>  }