linux-kernel - Re: [PATCH v2 2/2] serial: earlycon: allow to specify uartclk in earlycon kernel-parameter

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Date:	Tue, 20 Oct 2015 10:00:58 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:	linux-serial@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH v2 2/2] serial: earlycon: allow to specify uartclk in
 earlycon kernel-parameter

On 10/19/2015 11:36 PM, Masahiro Yamada wrote:
> The input clock frequency varies from device to device, but the
> earlycon uses the fixed frequency (BASE_BAUD * 16).  It makes
> impossible to set the correct divisor to the register.

So the bootloader hasn't setup the serial port?


> This commit allows to specify the input clock frequency from the
> kernel-parameter.
> 
> [Example]
> 
>     earlycon=uart8250,mmio32,0x43fb0000,115200,12288000
> 
> The input clock frequency (12288000, in this case) should be specified
> after the baudrate.  If not specified, the default (BASE_BAUD * 16) is
> used.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 
> Changes in v2: None
> 
>  drivers/tty/serial/earlycon.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index 07f7393..8030765 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -95,6 +95,13 @@ static int __init parse_options(struct earlycon_device *device, char *options)
>  		length = min(strcspn(options, " ") + 1,
>  			     (size_t)(sizeof(device->options)));
>  		strlcpy(device->options, options, length);
> +		options = strchr(options, ',');
> +		if (options) {
> +			options++;
> +			port->uartclk = simple_strtoul(options, NULL, 0);
> +		}
> +		if (!port->uartclk)
> +			port->uartclk = BASE_BAUD * 16;
>  	}
>  
>  	if (port->iotype == UPIO_MEM || port->iotype == UPIO_MEM16 ||
> @@ -122,7 +129,6 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
>  	if (buf && !parse_options(&early_console_dev, buf))
>  		buf = NULL;
>  
> -	port->uartclk = BASE_BAUD * 16;
>  	if (port->mapbase)
>  		port->membase = earlycon_map(port->mapbase, 64);
>  
> 

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