Subject: Re: [PATCH 1/5] arm_mpam: Parse the rest of the ACPI table

From: Ben Horgan <[email-masked]>
Date: Fri, 8 May 2026 11:21:20 +0100

Hi Andre,

On 4/29/26 15:13, Andre Przywara wrote:
> From: James Morse <[email-masked]>
> 
> The MPAM ACPI table lists the MPAM MSCs and indicates which resources
> in the system they control. Not everything this table can describe is
> supported by resctrl, e.g. memory-side-caches.
> 
> Add the additional table parsing to avoid reporting these as 'unknown'
> to the MPAM driver. This allows class+component hierarchys to be built.
> 
> Until resctrl has support for any of these resources, users would be
> in-kernel managers of a resource/PARTID or perf to query bandwidth
> counters on a resource resctrl is unaware of.

Does this patch give us anything needed for MPAM-Fb? It seems to just add
parsing for things we don't support in the MPAM driver.

Thanks,

Ben

> 
> Signed-off-by: James Morse <[email-masked]>
> Signed-off-by: Andre Przywara <[email-masked]>
> ---
>  drivers/acpi/arm64/mpam.c | 91 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 88 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
> index 84963a20c3e7..99c2bdbb3314 100644
> --- a/drivers/acpi/arm64/mpam.c
> +++ b/drivers/acpi/arm64/mpam.c
> @@ -95,17 +95,51 @@ static void acpi_mpam_parse_irqs(struct platform_device *pdev,
>  		res[(*res_idx)++] = DEFINE_RES_IRQ_NAMED(irq, "error");
>  }
>  
> -static int acpi_mpam_parse_resource(struct mpam_msc *msc,
> +#define UUID_MPAM_INTERCONNECT_TABLE		"fe2bd645-033b-49e6-9479-2e0b8b21d1cd"
> +
> +struct acpi_mpam_interconnect_descriptor_table {
> +	u8	type_uuid[16];
> +	u32	num_descriptors;
> +};
> +
> +struct acpi_mpam_interconnect_descriptor {
> +	u32	source_id;
> +	u32	destination_id;
> +	u8	link_type;
> +	u8	reserved[3];
> +};
> +
> +static int acpi_mpam_parse_resource(struct acpi_mpam_msc_node *tbl_msc,
> +				    struct mpam_msc *msc,
>  				    struct acpi_mpam_resource_node *res)
>  {
> +	struct acpi_mpam_interconnect_descriptor_table *tbl_int_tbl;
> +	struct acpi_mpam_interconnect_descriptor *tbl_int;
> +	guid_t int_tbl_uuid, spec_uuid;
>  	int level, nid;
>  	u32 cache_id;
> +	off_t offset;
>  
> +	/*
> +	 * Class IDs are somewhat arbitrary, but need to be co-ordinated.
> +	 * 0-N are caches,
> +	 * 64, 65: Interconnect, but ideally these would appear between the
> +	 *     classes the controls are adjacent to.
> +	 * 128: SMMU,
> +	 * 192-192+level: Memory Side Caches, nothing checks that N is a
> +	 *                small number.
> +	 * 255: Memory Controllers
> +	 *
> +	 * ACPI devices would need a class id allocated based on the _HID.
> +	 *
> +	 * Classes that the mpam driver can't currently plumb into resctrl
> +	 * are registered as UNKNOWN.
> +	 */
>  	switch (res->locator_type) {
>  	case ACPI_MPAM_LOCATION_TYPE_PROCESSOR_CACHE:
>  		cache_id = res->locator.cache_locator.cache_reference;
>  		level = find_acpi_cache_level_from_id(cache_id);
> -		if (level <= 0) {
> +		if (level <= 0 || level >= 64) {
>  			pr_err_once("Bad level (%d) for cache with id %u\n", level, cache_id);
>  			return -EINVAL;
>  		}
> @@ -120,6 +154,57 @@ static int acpi_mpam_parse_resource(struct mpam_msc *msc,
>  		}
>  		return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_MEMORY,
>  				       MPAM_CLASS_ID_DEFAULT, nid);
> +	case ACPI_MPAM_LOCATION_TYPE_SMMU:
> +		return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_UNKNOWN,
> +				       128, res->locator.smmu_locator.smmu_interface);
> +	case ACPI_MPAM_LOCATION_TYPE_MEMORY_CACHE:
> +		cache_id = res->locator.mem_cache_locator.reference;
> +		level = res->locator.mem_cache_locator.level;
> +		if (192 + level >= 255) {
> +			pr_err_once("Bad level for memory side cache with reference %u\n",
> +				    cache_id);
> +			return -EINVAL;
> +		}
> +
> +		return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_CACHE,
> +				       192 + level, cache_id);
> +
> +	case ACPI_MPAM_LOCATION_TYPE_INTERCONNECT:
> +		/* Find the descriptor table, and check it lands in the parent msc */
> +		offset = res->locator.interconnect_ifc_locator.inter_connect_desc_tbl_off;
> +		if (offset >= tbl_msc->length) {
> +			pr_err_once("Bad offset for interconnect descriptor on msc %u\n",
> +				    tbl_msc->identifier);
> +			return -EINVAL;
> +		}
> +		tbl_int_tbl = ACPI_ADD_PTR(struct acpi_mpam_interconnect_descriptor_table,
> +					   tbl_msc, offset);
> +		guid_parse(UUID_MPAM_INTERCONNECT_TABLE, &spec_uuid);
> +		import_guid(&int_tbl_uuid, tbl_int_tbl->type_uuid);
> +		if (guid_equal(&spec_uuid, &int_tbl_uuid)) {
> +			pr_err_once("Bad UUID for interconnect descriptor on msc %u\n",
> +				    tbl_msc->identifier);
> +			return -EINVAL;
> +		}
> +
> +		offset += sizeof(*tbl_int_tbl);
> +		offset += tbl_int_tbl->num_descriptors * sizeof(*tbl_int);
> +		if (offset >= tbl_msc->length) {
> +			pr_err_once("Bad num_descriptors for interconnect descriptor on msc %u\n",
> +				    tbl_msc->identifier);
> +			return -EINVAL;
> +		}
> +
> +		tbl_int = ACPI_ADD_PTR(struct acpi_mpam_interconnect_descriptor,
> +				       tbl_int_tbl, sizeof(*tbl_int_tbl));
> +		cache_id = tbl_int->source_id;
> +
> +		/* Unknown link type? */
> +		if (tbl_int->link_type != 0 && tbl_int->link_type == 1)
> +			return 0;
> +
> +		return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_UNKNOWN,
> +				       64 + tbl_int->link_type, cache_id);
>  	default:
>  		/* These get discovered later and are treated as unknown */
>  		return 0;
> @@ -150,7 +235,7 @@ int acpi_mpam_parse_resources(struct mpam_msc *msc,
>  			return -EINVAL;
>  		}
>  
> -		err = acpi_mpam_parse_resource(msc, resource);
> +		err = acpi_mpam_parse_resource(tbl_msc, msc, resource);
>  		if (err)
>  			return err;
>