Re: [PATCH v2 06/29] ACPI / MPAM: Parse the MPAM table

Gavin Shan
2025-10-03T00:58:57Z

On 9/11/25 6:42 AM, James Morse wrote:
> Add code to parse the arm64 specific MPAM table, looking up the cache
> level from the PPTT and feeding the end result into the MPAM driver.
>
> For now the MPAM hook mpam_ris_create() is stubbed out, but will update
> the MPAM driver with optional discovered data.
>
> CC: Carl Worth <carl@os.amperecomputing.com>
> Link: https://developer.arm.com/documentation/den0065/3-0bet/?lang=en
> Signed-off-by: James Morse <james.morse@arm.com>
>
> ---
> Changes since v1:
> * Whitespace.
> * Gave GLOBAL_AFFINITY a pre-processor'd name.
> * Fixed assumption that there are zero functional dependencies.
> * Bounds check walking of the MSC RIS.
> * More bounds checking in the main table walk.
> * Check for nonsense numbers of function dependencies.
> * Smattering of pr_debug() to help folk feeding line-noise to the parser.
> * Changed the comment flavour on the SPDX string.
> * Removed additional table check.
> * More comment wrangling.
>
> Changes since RFC:
> * Used DEFINE_RES_IRQ_NAMED() and friends macros.
> * Additional error handling.
> * Check for zero sized MSC.
> * Allow table revisions greater than 1. (no spec for revision 0!)
> * Use cleanup helpers to retrive ACPI tables, which allows some functions
> to be folded together.
> ---
> arch/arm64/Kconfig | 1 +
> drivers/acpi/arm64/Kconfig | 3 +
> drivers/acpi/arm64/Makefile | 1 +
> drivers/acpi/arm64/mpam.c | 361 ++++++++++++++++++++++++++++++++++++
> drivers/acpi/tables.c | 2 +-
> include/linux/acpi.h | 12 ++
> include/linux/arm_mpam.h | 48 +++++
> 7 files changed, 427 insertions(+), 1 deletion(-)
> create mode 100644 drivers/acpi/arm64/mpam.c
> create mode 100644 include/linux/arm_mpam.h
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 4be8a13505bf..6487c511bdc6 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -2062,6 +2062,7 @@ config ARM64_TLB_RANGE
>
> config ARM64_MPAM
> bool "Enable support for MPAM"
> + select ACPI_MPAM if ACPI
> help
> Memory System Resource Partitioning and Monitoring (MPAM) is an
> optional extension to the Arm architecture that allows each
> diff --git a/drivers/acpi/arm64/Kconfig b/drivers/acpi/arm64/Kconfig
> index b3ed6212244c..f2fd79f22e7d 100644
> --- a/drivers/acpi/arm64/Kconfig
> +++ b/drivers/acpi/arm64/Kconfig
> @@ -21,3 +21,6 @@ config ACPI_AGDI
>
> config ACPI_APMT
> bool
> +
> +config ACPI_MPAM
> + bool
> diff --git a/drivers/acpi/arm64/Makefile b/drivers/acpi/arm64/Makefile
> index 05ecde9eaabe..9390b57cb564 100644
> --- a/drivers/acpi/arm64/Makefile
> +++ b/drivers/acpi/arm64/Makefile
> @@ -4,6 +4,7 @@ obj-$(CONFIG_ACPI_APMT) += apmt.o
> obj-$(CONFIG_ACPI_FFH) += ffh.o
> obj-$(CONFIG_ACPI_GTDT) += gtdt.o
> obj-$(CONFIG_ACPI_IORT) += iort.o
> +obj-$(CONFIG_ACPI_MPAM) += mpam.o
> obj-$(CONFIG_ACPI_PROCESSOR_IDLE) += cpuidle.o
> obj-$(CONFIG_ARM_AMBA) += amba.o
> obj-y += dma.o init.o
> diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
> new file mode 100644
> index 000000000000..fd9cfa143676
> --- /dev/null
> +++ b/drivers/acpi/arm64/mpam.c
> @@ -0,0 +1,361 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2025 Arm Ltd.
> +
> +/* Parse the MPAM ACPI table feeding the discovered nodes into the driver */
> +
> +#define pr_fmt(fmt) "ACPI MPAM: " fmt
> +
> +#include <linux/acpi.h>
> +#include <linux/arm_mpam.h>
> +#include <linux/bits.h>
> +#include <linux/cpu.h>
> +#include <linux/cpumask.h>
> +#include <linux/platform_device.h>
> +
> +#include <acpi/processor.h>
> +
> +/*
> + * Flags for acpi_table_mpam_msc.*_interrupt_flags.
> + * See 2.1.1 Interrupt Flags, Table 5, of DEN0065B_MPAM_ACPI_3.0-bet.
> + */
> +#define ACPI_MPAM_MSC_IRQ_MODE_MASK BIT(0)
> +#define ACPI_MPAM_MSC_IRQ_TYPE_MASK GENMASK(2, 1)
> +#define ACPI_MPAM_MSC_IRQ_TYPE_WIRED 0
> +#define ACPI_MPAM_MSC_IRQ_AFFINITY_PROCESSOR_CONTAINER BIT(3)
> +#define ACPI_MPAM_MSC_IRQ_AFFINITY_VALID BIT(4)
> +
> +static bool acpi_mpam_register_irq(struct platform_device *pdev, int intid,
> + u32 flags, int *irq,
> + u32 processor_container_uid)
> +{
> + int sense;
> +
> + if (!intid)
> + return false;
> +
> + if (FIELD_GET(ACPI_MPAM_MSC_IRQ_TYPE_MASK, flags) !=
> + ACPI_MPAM_MSC_IRQ_TYPE_WIRED)
> + return false;
> +
> + sense = FIELD_GET(ACPI_MPAM_MSC_IRQ_MODE_MASK, flags);
> +
> + if (16 <= intid && intid < 32 && processor_container_uid != GLOBAL_AFFINITY) {
> + pr_err_once("Partitioned interrupts not supported\n");
> + return false;
> + }
> +
> + *irq = acpi_register_gsi(&pdev->dev, intid, sense, ACPI_ACTIVE_HIGH);
> + if (*irq <= 0) {
> + pr_err_once("Failed to register interrupt 0x%x with ACPI\n",
> + intid);
> + return false;
> + }
> +
> + return true;
> +}

0 is allowed by acpi_register_gsi().

if (*irq < 0) {
pr_err_once(...);
return false;
}

> +
> +static void acpi_mpam_parse_irqs(struct platform_device *pdev,
> + struct acpi_mpam_msc_node *tbl_msc,
> + struct resource *res, int *res_idx)
> +{
> + u32 flags, aff;
> + int irq;
> +
> + flags = tbl_msc->overflow_interrupt_flags;
> + if (flags & ACPI_MPAM_MSC_IRQ_AFFINITY_VALID &&
> + flags & ACPI_MPAM_MSC_IRQ_AFFINITY_PROCESSOR_CONTAINER)
> + aff = tbl_msc->overflow_interrupt_affinity;
> + else
> + aff = GLOBAL_AFFINITY;
> + if (acpi_mpam_register_irq(pdev, tbl_msc->overflow_interrupt, flags, &irq, aff))
> + res[(*res_idx)++] = DEFINE_RES_IRQ_NAMED(irq, "overflow");
> +
> + flags = tbl_msc->error_interrupt_flags;
> + if (flags & ACPI_MPAM_MSC_IRQ_AFFINITY_VALID &&
> + flags & ACPI_MPAM_MSC_IRQ_AFFINITY_PROCESSOR_CONTAINER)
> + aff = tbl_msc->error_interrupt_affinity;
> + else
> + aff = GLOBAL_AFFINITY;
> + if (acpi_mpam_register_irq(pdev, tbl_msc->error_interrupt, flags, &irq, aff))
> + res[(*res_idx)++] = DEFINE_RES_IRQ_NAMED(irq, "error");
> +}
> +
> +static int acpi_mpam_parse_resource(struct mpam_msc *msc,
> + struct acpi_mpam_resource_node *res)
> +{
> + int level, nid;
> + u32 cache_id;
> +
> + 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) {
> + pr_err_once("Bad level (%u) for cache with id %u\n", level, cache_id);
> + return -EINVAL;
> + }
> + return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_CACHE,
> + level, cache_id);
> + case ACPI_MPAM_LOCATION_TYPE_MEMORY:
> + nid = pxm_to_node(res->locator.memory_locator.proximity_domain);
> + if (nid == NUMA_NO_NODE)
> + nid = 0;
> + return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_MEMORY,
> + 255, nid);

It's perhaps worthy a warning message when @nid is explicitly set to zero due to
the bad proximity domain, something like below.

if (nid == NUMA_NO_NODE) {
nid = 0;
if (num_possible_nodes() > 1) {
pr_warn("Bad proximity domain %d, mapped to node 0\n",
res->locator.memory_locator.proximity_domain);
}
}

> + default:
> + /* These get discovered later and treated as unknown */
> + return 0;
> + }
> +}
> +
> +int acpi_mpam_parse_resources(struct mpam_msc *msc,
> + struct acpi_mpam_msc_node *tbl_msc)
> +{
> + int i, err;
> + char *ptr, *table_end;
> + struct acpi_mpam_resource_node *resource;
> +
> + ptr = (char *)(tbl_msc + 1);
> + table_end = ptr + tbl_msc->length;
> + for (i = 0; i < tbl_msc->num_resource_nodes; i++) {
> + u64 max_deps, remaining_table;
> +
> + if (ptr + sizeof(*resource) > table_end)
> + return -EINVAL;
> +
> + resource = (struct acpi_mpam_resource_node *)ptr;
> +
> + remaining_table = table_end - ptr;
> + max_deps = remaining_table / sizeof(struct acpi_mpam_func_deps);
> + if (resource->num_functional_deps > max_deps) {
> + pr_debug("MSC has impossible number of functional dependencies\n");
> + return -EINVAL;
> + }
> +
> + err = acpi_mpam_parse_resource(msc, resource);
> + if (err)
> + return err;
> +
> + ptr += sizeof(*resource);
> + ptr += resource->num_functional_deps * sizeof(struct acpi_mpam_func_deps);
> + }
> +
> + return 0;
> +}
> +
> +static bool __init parse_msc_pm_link(struct acpi_mpam_msc_node *tbl_msc,
> + struct platform_device *pdev,
> + u32 *acpi_id)
> +{
> + char hid[sizeof(tbl_msc->hardware_id_linked_device) + 1];
> + bool acpi_id_valid = false;
> + struct acpi_device *buddy;
> + char uid[11];
> + int err;
> +
> + memset(&hid, 0, sizeof(hid));
> + memcpy(hid, &tbl_msc->hardware_id_linked_device,
> + sizeof(tbl_msc->hardware_id_linked_device));
> +
> + if (!strcmp(hid, ACPI_PROCESSOR_CONTAINER_HID)) {
> + *acpi_id = tbl_msc->instance_id_linked_device;
> + acpi_id_valid = true;
> + }
> +
> + err = snprintf(uid, sizeof(uid), "%u",
> + tbl_msc->instance_id_linked_device);
> + if (err >= sizeof(uid)) {
> + pr_debug("Failed to convert uid of device for power management.");
> + return acpi_id_valid;
> + }
> +
> + buddy = acpi_dev_get_first_match_dev(hid, uid, -1);
> + if (buddy)
> + device_link_add(&pdev->dev, &buddy->dev, DL_FLAG_STATELESS);
> +
> + return acpi_id_valid;
> +}
> +
> +static int decode_interface_type(struct acpi_mpam_msc_node *tbl_msc,
> + enum mpam_msc_iface *iface)
> +{
> + switch (tbl_msc->interface_type) {
> + case 0:
> + *iface = MPAM_IFACE_MMIO;
> + return 0;
> + case 0xa:
> + *iface = MPAM_IFACE_PCC;
> + return 0;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +static int __init acpi_mpam_parse(void)
> +{
> + struct acpi_table_header *table __free(acpi_table) = acpi_get_table_ret(ACPI_SIG_MPAM, 0);
> + char *table_end, *table_offset = (char *)(table + 1);
> + struct property_entry props[4]; /* needs a sentinel */
> + struct acpi_mpam_msc_node *tbl_msc;
> + int next_res, next_prop, err = 0;
> + struct acpi_device *companion;
> + struct platform_device *pdev;
> + enum mpam_msc_iface iface;
> + struct resource res[3];
> + char uid[16];
> + u32 acpi_id;
> +
> + if (acpi_disabled || !system_supports_mpam() || IS_ERR(table))
> + return 0;
> +
> + if (table->revision < 1)
> + return 0;
> +
> + table_end = (char *)table + table->length;
> +
> + while (table_offset < table_end) {
> + tbl_msc = (struct acpi_mpam_msc_node *)table_offset;
> + table_offset += tbl_msc->length;
> +
> + if (table_offset > table_end) {
> + pr_debug("MSC entry overlaps end of ACPI table\n");
> + break;
> + }
> +
> + /*
> + * If any of the reserved fields are set, make no attempt to
> + * parse the MSC structure. This MSC will still be counted,
> + * meaning the MPAM driver can't probe against all MSC, and
> + * will never be enabled. There is no way to enable it safely,
> + * because we cannot determine safe system-wide partid and pmg
> + * ranges in this situation.
> + */
> + if (tbl_msc->reserved || tbl_msc->reserved1 || tbl_msc->reserved2) {
> + pr_err_once("Unrecognised MSC, MPAM not usable\n");
> + pr_debug("MSC.%u: reserved field set\n", tbl_msc->identifier);
> + continue;
> + }
> +
> + if (!tbl_msc->mmio_size) {
> + pr_debug("MSC.%u: marked as disabled\n", tbl_msc->identifier);
> + continue;
> + }
> +
> + if (decode_interface_type(tbl_msc, &iface)) {
> + pr_debug("MSC.%u: unknown interface type\n", tbl_msc->identifier);
> + continue;
> + }
> +
> + next_res = 0;
> + next_prop = 0;
> + memset(res, 0, sizeof(res));
> + memset(props, 0, sizeof(props));
> +
> + pdev = platform_device_alloc("mpam_msc", tbl_msc->identifier);
> + if (!pdev) {
> + err = -ENOMEM;
> + break;
> + }
> +
> + if (tbl_msc->length < sizeof(*tbl_msc)) {
> + err = -EINVAL;
> + break;
> + }
> +
> + /* Some power management is described in the namespace: */
> + err = snprintf(uid, sizeof(uid), "%u", tbl_msc->identifier);
> + if (err > 0 && err < sizeof(uid)) {
> + companion = acpi_dev_get_first_match_dev("ARMHAA5C", uid, -1);
> + if (companion)
> + ACPI_COMPANION_SET(&pdev->dev, companion);
> + else
> + pr_debug("MSC.%u: missing namespace entry\n", tbl_msc->identifier);
> + }
> +
> + if (iface == MPAM_IFACE_MMIO) {
> + res[next_res++] = DEFINE_RES_MEM_NAMED(tbl_msc->base_address,
> + tbl_msc->mmio_size,
> + "MPAM:MSC");
> + } else if (iface == MPAM_IFACE_PCC) {
> + props[next_prop++] = PROPERTY_ENTRY_U32("pcc-channel",
> + tbl_msc->base_address);
> + next_prop++;
> + }
> +
> + acpi_mpam_parse_irqs(pdev, tbl_msc, res, &next_res);
> + err = platform_device_add_resources(pdev, res, next_res);
> + if (err)
> + break;
> +
> + props[next_prop++] = PROPERTY_ENTRY_U32("arm,not-ready-us",
> + tbl_msc->max_nrdy_usec);
> +
> + /*
> + * The MSC's CPU affinity is described via its linked power
> + * management device, but only if it points at a Processor or
> + * Processor Container.
> + */
> + if (parse_msc_pm_link(tbl_msc, pdev, &acpi_id)) {
> + props[next_prop++] = PROPERTY_ENTRY_U32("cpu_affinity",
> + acpi_id);
> + }
> +
> + err = device_create_managed_software_node(&pdev->dev, props,
> + NULL);
> + if (err)
> + break;
> +
> + /* Come back later if you want the RIS too */
> + err = platform_device_add_data(pdev, tbl_msc, tbl_msc->length);
> + if (err)
> + break;
> +
> + err = platform_device_add(pdev);
> + if (err)
> + break;
> + }
> +
> + if (err)
> + platform_device_put(pdev);
> +
> + return err;
> +}
> +
> +int acpi_mpam_count_msc(void)
> +{
> + struct acpi_table_header *table __free(acpi_table) = acpi_get_table_ret(ACPI_SIG_MPAM, 0);
> + char *table_end, *table_offset = (char *)(table + 1);
> + struct acpi_mpam_msc_node *tbl_msc;
> + int count = 0;
> +
> + if (IS_ERR(table))
> + return 0;
> +
> + if (table->revision < 1)
> + return 0;
> +
> + table_end = (char *)table + table->length;
> +
> + while (table_offset < table_end) {
> + tbl_msc = (struct acpi_mpam_msc_node *)table_offset;
> + if (!tbl_msc->mmio_size)
> + continue;
> +
> + if (tbl_msc->length < sizeof(*tbl_msc))
> + return -EINVAL;
> + if (tbl_msc->length > table_end - table_offset)
> + return -EINVAL;
> + table_offset += tbl_msc->length;
> +
> + count++;
> + }
> +
> + return count;
> +}
> +

acpi_mpam_count_msc() iterates the existing MSC node, which is part of acpi_mpam_parse().
So the question is why we can't drop acpi_mpam_count_msc() and maintain a variable to
count the existing MSC nodes in acpi_mpam_parse() ?

> +/*
> + * Call after ACPI devices have been created, which happens behind acpi_scan_init()
> + * called from subsys_initcall(). PCC requires the mailbox driver, which is
> + * initialised from postcore_initcall().
> + */
> +subsys_initcall_sync(acpi_mpam_parse);
> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index fa9bb8c8ce95..835e3795ede3 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -408,7 +408,7 @@ static const char table_sigs[][ACPI_NAMESEG_SIZE] __nonstring_array __initconst
> ACPI_SIG_PSDT, ACPI_SIG_RSDT, ACPI_SIG_XSDT, ACPI_SIG_SSDT,
> ACPI_SIG_IORT, ACPI_SIG_NFIT, ACPI_SIG_HMAT, ACPI_SIG_PPTT,
> ACPI_SIG_NHLT, ACPI_SIG_AEST, ACPI_SIG_CEDT, ACPI_SIG_AGDI,
> - ACPI_SIG_NBFT };
> + ACPI_SIG_NBFT, ACPI_SIG_MPAM };
>
> #define ACPI_HEADER_SIZE sizeof(struct acpi_table_header)
>
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index c5fd92cda487..af449964426b 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -8,6 +8,7 @@
> #ifndef _LINUX_ACPI_H
> #define _LINUX_ACPI_H
>
> +#include <linux/cleanup.h>
> #include <linux/errno.h>
> #include <linux/ioport.h> /* for struct resource */
> #include <linux/resource_ext.h>
> @@ -221,6 +222,17 @@ void acpi_reserve_initial_tables (void);
> void acpi_table_init_complete (void);
> int acpi_table_init (void);
>
> +static inline struct acpi_table_header *acpi_get_table_ret(char *signature, u32 instance)
> +{
> + struct acpi_table_header *table;
> + int status = acpi_get_table(signature, instance, &table);
> +
> + if (ACPI_FAILURE(status))
> + return ERR_PTR(-ENOENT);
> + return table;
> +}
> +DEFINE_FREE(acpi_table, struct acpi_table_header *, if (!IS_ERR(_T)) acpi_put_table(_T))
> +
> int acpi_table_parse(char *id, acpi_tbl_table_handler handler);
> int __init_or_acpilib acpi_table_parse_entries(char *id,
> unsigned long table_size, int entry_id,
> diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
> new file mode 100644
> index 000000000000..3d6c39c667c3
> --- /dev/null
> +++ b/include/linux/arm_mpam.h
> @@ -0,0 +1,48 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2025 Arm Ltd. */
> +
> +#ifndef __LINUX_ARM_MPAM_H
> +#define __LINUX_ARM_MPAM_H
> +
> +#include <linux/acpi.h>
> +#include <linux/types.h>
> +
> +#define GLOBAL_AFFINITY ~0
> +
> +struct mpam_msc;
> +
> +enum mpam_msc_iface {
> + MPAM_IFACE_MMIO, /* a real MPAM MSC */
> + MPAM_IFACE_PCC, /* a fake MPAM MSC */
> +};
> +
> +enum mpam_class_types {
> + MPAM_CLASS_CACHE, /* Well known caches, e.g. L2 */
> + MPAM_CLASS_MEMORY, /* Main memory */
> + MPAM_CLASS_UNKNOWN, /* Everything else, e.g. SMMU */
> +};
> +
> +#ifdef CONFIG_ACPI_MPAM
> +/* Parse the ACPI description of resources entries for this MSC. */
> +int acpi_mpam_parse_resources(struct mpam_msc *msc,
> + struct acpi_mpam_msc_node *tbl_msc);
> +
> +int acpi_mpam_count_msc(void);
> +#else
> +static inline int acpi_mpam_parse_resources(struct mpam_msc *msc,
> + struct acpi_mpam_msc_node *tbl_msc)
> +{
> + return -EINVAL;
> +}
> +
> +static inline int acpi_mpam_count_msc(void) { return -EINVAL; }
> +#endif
> +
> +static inline int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
> + enum mpam_class_types type, u8 class_id,
> + int component_id)
> +{
> + return -EINVAL;
> +}
> +
> +#endif /* __LINUX_ARM_MPAM_H */

Thanks,
Gavin