Re: [PATCH RFC 1/7] ACPICA: Define PCIe P2P latency and bandwidth information

On Wed, Aug 12, 2026 at 9:48 PM Leon Romanovsky <[email protected]> wrote:
>
> From: Leon Romanovsky <[email protected]>
>
> PCIe topology alone cannot tell an operating system whether traffic may
> cross host bridges, what ordering rules it needs, or how expensive the path
> is. Encoding this knowledge in chipset lists duplicates platform policy and
> cannot survive a virtualized topology.
>
> Define HMAT Type 3 as a firmware contract for directional Generic Port P2P
> paths, including separate ordered and Unordered I/O applicability. This
> gives platform software a standard way to distinguish unsupported,
> conditional, and usable paths. The definition follows a proposed ACPI ECN.
>
> Signed-off-by: Leon Romanovsky <[email protected]>
> ---
>  include/acpi/actbl1.h | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)

As per Documentation/driver-api/acpi/linuxized-acpica.rst, please
submit a pull request with this change to the upstream ACPICA project
on GitHub.  The Linux patch will become applicable when there is a
corresponding commit upstream.

> diff --git a/include/acpi/actbl1.h b/include/acpi/actbl1.h
> index d824838cb7af..0fc766a8e90f 100644
> --- a/include/acpi/actbl1.h
> +++ b/include/acpi/actbl1.h
> @@ -2003,7 +2003,8 @@ enum acpi_hmat_type {
>         ACPI_HMAT_TYPE_PROXIMITY = 0,   /* Memory proximity domain attributes */
>         ACPI_HMAT_TYPE_LOCALITY = 1,    /* System locality latency and bandwidth information */
>         ACPI_HMAT_TYPE_CACHE = 2,       /* Memory side cache information */
> -       ACPI_HMAT_TYPE_RESERVED = 3     /* 3 and greater are reserved */
> +       ACPI_HMAT_TYPE_P2P_LATENCY = 3, /* PCIe P2P latency and bandwidth information */
> +       ACPI_HMAT_TYPE_RESERVED = 4     /* 4 and greater are reserved */
>  };
>
>  struct acpi_hmat_structure {
> @@ -2108,6 +2109,30 @@ struct acpi_hmat_cache {
>  #define ACPI_HMAT_CP_WB     (1)
>  #define ACPI_HMAT_CP_WT     (2)
>
> +/* 3: PCIe P2P Latency and Bandwidth Information */
> +
> +struct acpi_hmat_p2p_latency {
> +       struct acpi_hmat_structure header;
> +       u8 flags;
> +       u8 data_type;
> +       u16 reserved1;
> +       u32 number_of_initiator_Pds;
> +       u32 number_of_target_Pds;
> +       u32 reserved2;
> +       u64 entry_base_unit;
> +};
> +
> +/* Masks for Flags field above */
> +
> +#define ACPI_HMAT_P2P_NON_UIO   (1)    /* Bit 0: Entries apply to non-UIO traffic */
> +#define ACPI_HMAT_P2P_UIO       (1<<1) /* Bit 1: Entries apply to UIO traffic */
> +
> +/*
> + * The data_type field reuses the ACPI_HMAT_ACCESS/READ/WRITE_LATENCY and
> + * ACPI_HMAT_ACCESS/READ/WRITE_BANDWIDTH values defined for the System
> + * Locality Latency and Bandwidth Information Structure above.
> + */
> +
>  /*******************************************************************************
>   *
>   * HPET - High Precision Event Timer table
>
> --
> 2.55.0
>