[PATCH v3 10/11] qfw: fix RSDP ext_checksum recomputation

[Ilias Apalodimas]

On Sun, 28 Jun 2026 at 11:28, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
> table_compute_checksum() returns the value that makes the byte sum of
> the buffer zero. If the ext_checksum field already contains a non-zero
> value (as QEMU's firmware-provided RSDP does), adding that existing
> value into the sum produces an incorrect complement. Zero the field
> before calling table_compute_checksum() so the calculation starts from
> a clean state, matching the pattern used in acpi_write_rsdp().
>
> Reviewed-by: Simon Glass <sjg at chromium.org>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>

Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>

> ---
> v3:
>         no change
> v2
>         new patch
> ---
>  drivers/misc/qfw_acpi.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/misc/qfw_acpi.c b/drivers/misc/qfw_acpi.c
> index 721f42ecbc3..afa3b820395 100644
> --- a/drivers/misc/qfw_acpi.c
> +++ b/drivers/misc/qfw_acpi.c
> @@ -265,6 +265,7 @@ out:
>         struct acpi_rsdp *rsdp = ctx->rsdp;
>
>         rsdp->length = sizeof(*rsdp);
> +       rsdp->ext_checksum = 0;
>         rsdp->ext_checksum = table_compute_checksum((u8 *)rsdp, sizeof(*rsdp));
>
>         gd_set_acpi_start(acpi_get_rsdp_addr());
> --
> 2.53.0
>