Re: [PATCH v5] serial: coreboot: Accept DBG2 subtype 0x12

Hi Desapogu,

On Wed, 29 Jul 2026 at 21:43, Desapogu Jayaramudu
<[email protected]> 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 <[email protected]>
> ---
> v5:
> - removed whitespce
>
>  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..89da11ffa5241e 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..ac50ea10312e28 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_16550_WITH_GAS       0x0012 /* 16550-compatible UART with GAS */
>
>  #define ACPI_DBG2_1394_STANDARD                0x0000
>
> --
> 2.43.0
>

I added my review tag to v4 - the idea is that you collect that tag
and send it out with the next version, unless you make major changes
etc. Here it is again:

Reviewed-by: Simon Glass <[email protected]>

Note that you don't need to send a v6 with this tag, since patchwork
will pick it up - you only need to collect the tag (e.g. manually, or
with 'patman series gather') when you need to send a new version with
changes. You probably already know this, sorry if so :-)

Regards,
Simon