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

Hi James, Jonathan,

On 7/16/25 18:07, Jonathan Cameron wrote:

On Fri, 11 Jul 2025 18:36:22 +0000
James Morse [off-list ref] wrote:

quoted

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.

Throw in a link to the spec perhaps?  Particularly useful to know which
version this was written against when reviewing it.

As I comment below this code checks the table revision is 1 and so we 
can assume it was written against version 2 of the spec. As of Monday, 
there is a new version hot off the press,
https://developer.arm.com/documentation/den0065/3-0bet/?lang=en which 
introduces an "MMIO size" field to allow for disabled nodes. This should 
be considered here to avoid advertising msc that aren't present.

quoted

CC: Carl Worth <redacted>
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

quoted

diff --git a/drivers/acpi/arm64/Makefile b/drivers/acpi/arm64/Makefile
index 05ecde9eaabe..27b872249baa 100644
--- a/drivers/acpi/arm64/Makefile
+++ b/drivers/acpi/arm64/Makefile

@@ -6,5 +6,6 @@ obj-$(CONFIG_ACPI_GTDT) 	+= gtdt.o
  obj-$(CONFIG_ACPI_IORT) 	+= iort.o
  obj-$(CONFIG_ACPI_PROCESSOR_IDLE) += cpuidle.o
  obj-$(CONFIG_ARM_AMBA)		+= amba.o
+obj-$(CONFIG_ACPI_MPAM) 	+= mpam.o

Keep it with the ACPI ones?  There doesn't seem to be a lot of order in here
though so I guess maybe there is logic behind putting it here I'm missing.

quoted

  obj-y				+= dma.o init.o
  obj-y				+= thermal_cpufreq.o

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 */

References.. I'm looking at 3.0-alpha table 5 to check this.
I can see why you might be reluctant to point at an alpha if that
is what you are using ;)

quoted

+#define ACPI_MPAM_MSC_IRQ_MODE_EDGE                    1
+#define ACPI_MPAM_MSC_IRQ_TYPE_MASK                    (3 << 1)

GENMASK(3, 2) would be my preference for how to do masks in new code.

quoted

+#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)

I'd prefer more explicit code (and probably no comment)

	if (FIELD_GET(flags, ACPI_MPAM_MSC_IRQ_TYPE_MASK) !=
	    ACPI_MPAM_MSC_IRQ_TYPE_WIRED)
		return false;

quoted

+		return false;
+
+	if (flags & ACPI_MPAM_MSC_IRQ_MODE_EDGE)
+		sense = ACPI_EDGE_SENSITIVE;
+	else
+		sense = ACPI_LEVEL_SENSITIVE;

If the spec is supposed to be using standard ACPI_* types for this field
(I don't think the connection is explicitly documented though) then

	sense = FIELD_GET(flags, ACPI_MPAM_MSC_IRQ_MODE_MASK);
Assuming a change to define the mask and rely on the ACPI defs for the values

This one is entirely up to you.

quoted

+
+	/*
+	 * 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;

Just to make the two cases look the same I'd do

	else
		aff = ~0;

here as well and not initialize above.  It's not quite worth using
a helper function for these two identical blocks but it's close.

quoted

+	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[*res_idx] = DEFINE_RES_IRQ_NAMED(irq, 1, "overflow");

quoted

+
+		(*res_idx)++;

Can roll this in as well.

quoted

+	}
+
+	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";

Similar to above.

quoted

+
+		(*res_idx)++;
+	}
+}
+

quoted

+static bool __init parse_msc_pm_link(struct acpi_mpam_msc_node *tbl_msc,
+				     struct platform_device *pdev,
+				     u32 *acpi_id)
+{
+	bool acpi_id_valid = false;
+	struct acpi_device *buddy;
+	char hid[16], uid[16];
+	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 < 0 || err >= sizeof(uid))

Does snprintf() ever return < 0 ?  It's documented as returning
number of chars printed (without the NULL) so that can only be 0 or
greater.

Can it return >= sizeof(uid) ? Looks odd.

+		return acpi_id_valid;

quoted

+
+	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;
+}

quoted

+static int __init _parse_table(struct acpi_table_header *table)
+{
+	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;
+
+	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 any of the reserved fields are set, make no attempt to
+		 * parse the msc structure. This will prevent the driver from
+		 * probing all the MSC, meaning it can't discover the system
+		 * wide supported partid and pmg ranges. This avoids whatever
+		 * this MSC is truncating the partids and creating a screaming
+		 * error interrupt.
+		 */
+		if (tbl_msc->reserved || tbl_msc->reserved1 || tbl_msc->reserved2)
+			continue;
+
+		if (decode_interface_type(tbl_msc, &iface))
+			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 (IS_ERR(pdev)) {

returns NULL in at least some error cases (probably all, I'm just to lazy to check)

quoted

+			err = PTR_ERR(pdev);
+			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);
+		}
+
+		if (iface == MPAM_IFACE_MMIO) {
+			res[next_res].name = "MPAM:MSC";
+			res[next_res].start = tbl_msc->base_address;
+			res[next_res].end = tbl_msc->base_address + tbl_msc->mmio_size - 1;
+			res[next_res].flags = IORESOURCE_MEM;
+			next_res++;

DEFINE_RES_MEM_NAMED()?

quoted

+		} 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;
+
+		platform_device_add(pdev);

Can fail.

quoted

+	}
+
+	if (err)
+		platform_device_put(pdev);
+
+	return err;
+}
+
+static struct acpi_table_header *get_table(void)
+{
+	struct acpi_table_header *table;
+	acpi_status status;
+
+	if (acpi_disabled || !system_supports_mpam())
+		return NULL;
+
+	status = acpi_get_table(ACPI_SIG_MPAM, 0, &table);
+	if (ACPI_FAILURE(status))
+		return NULL;
+
+	if (table->revision != 1)
+		return NULL;

Indicates that this was written against version 2 of the spec.

quoted

+
+	return table;
+}
+
+static int __init acpi_mpam_parse(void)
+{
+	struct acpi_table_header *mpam;
+	int err;
+
+	mpam = get_table();
+	if (!mpam)
+		return 0;

Just what I was suggesting for the PPTT case in early patches. Nice :)

quoted

+
+	err = _parse_table(mpam);
+	acpi_put_table(mpam);
+
+	return err;
+}
+
+static int _count_msc(struct acpi_table_header *table)
+{
+	char *table_end, *table_offset = (char *)(table + 1);
+	struct acpi_mpam_msc_node *tbl_msc;
+	int ret = 0;

Call it count as it only ever contains the count?

quoted

+
+	tbl_msc = (struct acpi_mpam_msc_node *)table_offset;
+	table_end = (char *)table + table->length;
+
+	while (table_offset < table_end) {
+		if (tbl_msc->length < sizeof(*tbl_msc))
+			return -EINVAL;
+
+		ret++;

count++ would feel more natural here.

quoted

+
+		table_offset += tbl_msc->length;
+		tbl_msc = (struct acpi_mpam_msc_node *)table_offset;
+	}
+
+	return ret;
+}

That's all I have time for today. Will get to the rest of the series soonish.

Jonathan

Thanks,

Ben