Re: [PATCH v3 2/2] ACPI: SPCR: Support UART clock frequency field

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Jun 15, 2026 at 12:40:22AM +0000, Markus Probst wrote:
> The Microsoft Serial Port Console Redirection (SPCR) specification
> revision 1.08 comprises additional field: UART Clock Frequency [1].
> 
> It contains a non-zero value indicating the UART clock frequency in Hz.

Ok, but then what are we going to do with this?  Please make this a lot
more descriptive, I have no idea what this is supposed to be doing at
all.

> 
> Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table [1]
> Signed-off-by: Markus Probst <markus.probst@posteo.de>
> ---
>  drivers/acpi/spcr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> index 73cb933fdc89..c79c809f49d4 100644
> --- a/drivers/acpi/spcr.c
> +++ b/drivers/acpi/spcr.c
> @@ -228,7 +228,8 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
>  	pr_info("console: %s\n", opts);
>  
>  	if (enable_earlycon)
> -		setup_earlycon(opts);
> +		setup_earlycon_with_uartclk(opts,
> +					    table->header.revision >= 3 ? table->uart_clk_freq : 0);

Why the magic number 3?

thanks,
greg k-h