Re: [RFC PATCH 10/36] ACPI / MPAM: Parse the MPAM table

[Ben Horgan <ben.horgan@arm.com>]

Hi James,

On 11/07/2025 19:36, 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.
> 
> CC: Carl Worth <carl@os.amperecomputing.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>   arch/arm64/Kconfig          |   1 +
>   drivers/acpi/arm64/Kconfig  |   3 +
>   drivers/acpi/arm64/Makefile |   1 +
>   drivers/acpi/arm64/mpam.c   | 365 ++++++++++++++++++++++++++++++++++++
>   drivers/acpi/tables.c       |   2 +-
>   include/linux/arm_mpam.h    |  46 +++++
>   6 files changed, 417 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/acpi/arm64/mpam.c
>   create mode 100644 include/linux/arm_mpam.h
[snip]
> diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
> new file mode 100644
> index 000000000000..f4791bac9a2a
> --- /dev/null
> +++ b/drivers/acpi/arm64/mpam.c
> @@ -0,0 +1,365 @@
> +// 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/cpu.h>
> +#include <linux/cpumask.h>
> +#include <linux/platform_device.h>
> +
> +#include <acpi/processor.h>
> +
> +/* Flags for acpi_table_mpam_msc.*_interrupt_flags */
> +#define ACPI_MPAM_MSC_IRQ_MODE_EDGE                    1
> +#define ACPI_MPAM_MSC_IRQ_TYPE_MASK                    (3 << 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 frob_irq(struct platform_device *pdev, int intid, u32 flags,
> +		     int *irq, u32 processor_container_uid)
> +{
> +	int sense;
> +
> +	if (!intid)
> +		return false;
> +
> +	/* 0 in this field indicates a wired interrupt */
> +	if (flags & ACPI_MPAM_MSC_IRQ_TYPE_MASK)
> +		return false;
> +
> +	if (flags & ACPI_MPAM_MSC_IRQ_MODE_EDGE)
> +		sense = ACPI_EDGE_SENSITIVE;
> +	else
> +		sense = ACPI_LEVEL_SENSITIVE;
> +
> +	/*
> +	 * If the GSI is in the GIC's PPI range, try and create a partitioned
> +	 * percpu interrupt.
> +	 */
> +	if (16 <= intid && intid < 32 && processor_container_uid != ~0) {
> +		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;
> +}
> +
> +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 = ~0;
> +	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;
> +	if (frob_irq(pdev, tbl_msc->overflow_interrupt, flags, &irq, aff)) {
> +		res[*res_idx].start = irq;
> +		res[*res_idx].end = irq;
> +		res[*res_idx].flags = IORESOURCE_IRQ;
> +		res[*res_idx].name = "overflow";
> +
> +		(*res_idx)++;
> +	}
> +
> +	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 = ~0;
> +	if (frob_irq(pdev, tbl_msc->error_interrupt, flags, &irq, aff)) {
> +		res[*res_idx].start = irq;
> +		res[*res_idx].end = irq;
> +		res[*res_idx].flags = IORESOURCE_IRQ;
> +		res[*res_idx].name = "error";
> +
> +		(*res_idx)++;
> +	}
> +}
> +
> +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;
Nit: More robust to check for level <= 0.

Thanks,

Ben