Re: [PATCH v2 2/3] serial: 8250_early: prepare for dynamic BASE_BAUD

[Peter Hurley <peter@hurleysoftware.com>]

Hi Vineet,

On 01/05/2015 06:30 AM, Vineet Gupta wrote:
> BASE_BAUD is pain in neck for multi-platform support as it hard codes at
> build time the clk value for early uart.
> 
> Mitigate this by allowing arches/platforms to provide their own version
> which can do dynamic setup based on DT values etc (see next patch for
> usage)
> 
> This was needed for ARC SDP platforms based on 2 different FPGA flows, each
> with a different UART clk value.
> 
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jiri Slaby <jslaby@suse.cz>
> Cc: linux-serial@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: Rob Herring <robh@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/tty/serial/earlycon.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index 64fe25a4285c..bfd3537739e0 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -54,6 +54,15 @@ static void __iomem * __init earlycon_map(unsigned long paddr, size_t size)
>  	return base;
>  }
>  
> +unsigned int __weak __init earlycon_base_baud(char *options)
> +{
> +#ifdef BASE_BAUD
> +	return BASE_BAUD;
> +#else
> +	return 1843200/16;	/* x86 early console */
> +#endif
> +}
> +
>  static int __init parse_options(struct earlycon_device *device,
>  				char *options)
>  {
> @@ -87,7 +96,7 @@ static int __init parse_options(struct earlycon_device *device,
>  		return -EINVAL;
>  	}
>  
> -	port->uartclk = BASE_BAUD * 16;
> +	port->uartclk = earlycon_base_baud(options) * 16;

I don't understand why BASE_BAUD can't be defined by arc as arc_earlycon_base_baud().
Why is the weak binding necessary?

I'm pushing back on this because port initialization (and especially 8250)
is already a ridiculous spiderweb.

Regards,
Peter Hurley

>  	options = strchr(options, ',');
>  	if (options) {
> @@ -156,7 +165,7 @@ int __init of_setup_earlycon(unsigned long addr,
>  
>  	port->iotype = UPIO_MEM;
>  	port->mapbase = addr;
> -	port->uartclk = BASE_BAUD * 16;
> +	port->uartclk = earlycon_base_baud(NULL) * 16;
>  	port->membase = earlycon_map(addr, SZ_4K);
>  
>  	early_console_dev.con->data = &early_console_dev;
>