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

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

Hi James, Jonathan,

On 7/16/25 18:07, Jonathan Cameron wrote:
> On Fri, 11 Jul 2025 18:36:22 +0000
> James Morse <james.morse@arm.com> 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.
> 
> 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.
> 
>>
>> 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
>>
> 
>> 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.
> 
>>   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 ;)
> 
> 
>> +#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.
> 
>> +#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;
> 
>> +		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.
> 
>> +
>> +	/*
>> +	 * 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.
> 
>> +	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");
>> +
>> +		(*res_idx)++;
> Can roll this in as well.
> 
>> +	}
>> +
>> +	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.
> 
>> +
>> +		(*res_idx)++;
>> +	}
>> +}
>> +
> 
> 
>> +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;
>> +
>> +	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 __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)
> 
>> +			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()?
> 
>> +		} 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.
> 
>> +	}
>> +
>> +	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.
>> +
>> +	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 :)
> 
>> +
>> +	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?
> 
>> +
>> +	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.
> 
>> +
>> +		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