Re: [PATCH v3] serial: coreboot: Accept DBG2 subtype 0x12

[Tom Rini <trini@konsulko.com>]

[-- Attachment #1: Type: text/plain, Size: 2727 bytes --]

On Mon, Jul 20, 2026 at 09:18:26PM +0530, Desapogu Jayaramudu wrote:
> U-Boot running as a coreboot payload obtains serial console
> information either from the coreboot table or from the ACPI DBG2
> table.
> 
> When serial console support is disabled in coreboot, the coreboot
> table does not contain serial information. In this case U-Boot falls
> back to parsing the DBG2 table.
> 
> Some AMD platforms or any other platforms that uses memory-mapped I/O
> advertise the debug UART using DBG2 subtype 0x0012 ("16550-compatible
> with parameters defined in Generic Address Structure"). U-Boot
> currently accepts only subtype 0x0000, causing DBG2 UART detection to
> fail and leaving no console output.
> 
> Accept subtype 0x0012 as well and keep the existing handling logic.
> 
> Signed-off-by: Desapogu Jayaramudu <jayaramudu.desapogu@amd.com>
> ---
> v3:
> - Change subject prefix to "serial: coreboot:"
> - Shorten commit subject
> - Remove extra From: line by fixing git author identity
> - Rework commit message formatting and wrapping
> - Rename subtype constant to ACPI_DBG2_16550_WITH_GAS
> - Add comment describing DBG2 subtype 0x12
> - Keep subtype definitions sorted by value
> - Wrap long conditional to stay within 80 columns
> 
>  drivers/serial/serial_coreboot.c | 3 ++-
>  include/acpi/acpi_table.h        | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/serial/serial_coreboot.c b/drivers/serial/serial_coreboot.c
> index b1f69f6998cfa1..cb07173a80c0cc 100644
> --- a/drivers/serial/serial_coreboot.c
> +++ b/drivers/serial/serial_coreboot.c
> @@ -59,7 +59,8 @@ static int read_dbg2(struct ns16550_plat *plat)
>  		log_debug("Not a serial port\n");
>  		return -EPROTOTYPE;
>  	}
> -	if (dbg->port_subtype != ACPI_DBG2_16550_COMPATIBLE) {
> +	if (dbg->port_subtype != ACPI_DBG2_16550_COMPATIBLE &&
> +            dbg->port_subtype != ACPI_DBG2_16550_WITH_GAS) {
>  		log_debug("Incompatible serial port\n");
>  		return -EPROTOTYPE;
>  	}
> diff --git a/include/acpi/acpi_table.h b/include/acpi/acpi_table.h
> index 4895366a6188ec..825652798166a4 100644
> --- a/include/acpi/acpi_table.h
> +++ b/include/acpi/acpi_table.h
> @@ -674,6 +674,7 @@ struct __packed acpi_dmar {
>  #define ACPI_DBG2_ARM_SBSA_GENERIC	0x000E
>  #define ACPI_DBG2_ARM_DCC		0x000F
>  #define ACPI_DBG2_BCM2835		0x0010
> +#define ACPI_DBG2_WITH_GAS		0x0012 /* 16550-compatible UART with GAS */
>  
>  #define ACPI_DBG2_1394_STANDARD		0x0000

This doesn't compile now. You reference ACPI_DBG2_16550_WITH_GAS and add
ACPI_DBG2_WITH_GAS so can you please do a v4 which compiles and you've
tested still resolves the issue? Thanks.

-- 
Tom

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]