[PATCH 0/4] perf/arm_cspmu: Miscellaneous improvements

[PATCH 0/4] perf/arm_cspmu: Miscellaneous improvements

[Robin Murphy]

Hi all,

These are a few quality-of-life improvements for CoreSight PMU that
I've accumulated based on things which have come up in practical usage.
There's no real dependency between any of the individual patches, it
just felt right to send them as a series.

Thanks,
Robin.


Robin Murphy (4):
  ACPI/APMT: Use stable device ID
  perf/arm_cspmu: Improve APMT-based PMU naming
  perf/arm_cspmu: Improve sub-module error reporting
  perf/arm_cspmu: Make IRQ more optional

 drivers/acpi/arm64/apmt.c          |  2 +-
 drivers/perf/arm_cspmu/arm_cspmu.c | 49 ++++++++++++++++++------------
 2 files changed, 31 insertions(+), 20 deletions(-)

-- 
2.54.0.dirty

[PATCH 1/4] ACPI/APMT: Use stable device ID

[Robin Murphy]

The APMT node format includes a unique identifier, so we can use this as
the platform device ID to give userspace stable and identifiable device
names, rather than auto numbering dependent on how the table is parsed.

Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Sudeep Holla <sudeep.holla@kernel.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/acpi/arm64/apmt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/arm64/apmt.c b/drivers/acpi/arm64/apmt.c
index bb010f6164e5..ba48fcb26d52 100644
--- a/drivers/acpi/arm64/apmt.c
+++ b/drivers/acpi/arm64/apmt.c
@@ -79,7 +79,7 @@ static int __init apmt_add_platform_device(struct acpi_apmt_node *node,
 	int ret, count;
 	struct resource res[DEV_MAX_RESOURCE_COUNT];
 
-	pdev = platform_device_alloc(DEV_NAME, PLATFORM_DEVID_AUTO);
+	pdev = platform_device_alloc(DEV_NAME, node->id);
 	if (!pdev)
 		return -ENOMEM;
 
-- 
2.54.0.dirty

[PATCH 2/4] perf/arm_cspmu: Improve APMT-based PMU naming

[Robin Murphy]

On ACPI systems, it has not actually been possible for userspace to
reliably tell which PMU corresponds to which APMT entry for types
other than "ACPI device" - the evidence trail only leads from the
arbitrarily-numbered PMU device to its arbitrarily-numbered parent
platform device that has no distinguishing features either.

While we've now improved the platform device creation to associate the
actual APMT unique ID, we may as well also tweak the PMU devices to
substitute the arbitrary number with a different arbitrary number that
might be more directly meaningful based on the APMT definitions.

We don't have an equivalent for Devicetree, but in that case the
platform devices are at least identifiable via their sysfs-visible
of_node.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/perf/arm_cspmu/arm_cspmu.c | 36 +++++++++++++++++-------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
index 80fb314d5135..0570be74d11f 100644
--- a/drivers/perf/arm_cspmu/arm_cspmu.c
+++ b/drivers/perf/arm_cspmu/arm_cspmu.c
@@ -250,38 +250,44 @@ static const char *arm_cspmu_get_name(const struct arm_cspmu *cspmu)
 	struct device *dev;
 	struct acpi_apmt_node *apmt_node;
 	u8 pmu_type;
-	char *name;
 	char acpi_hid_string[ACPI_ID_LEN] = { 0 };
-	static atomic_t pmu_idx[ACPI_APMT_NODE_TYPE_COUNT] = { 0 };
+	static atomic_t pmu_idx;
+	u32 id;
 
 	dev = cspmu->dev;
 	apmt_node = arm_cspmu_apmt_node(dev);
 	if (!apmt_node)
 		return devm_kasprintf(dev, GFP_KERNEL, PMUNAME "_%u",
-				      atomic_fetch_inc(&pmu_idx[0]));
+				      atomic_fetch_inc(&pmu_idx));
 
 	pmu_type = apmt_node->type;
-
-	if (pmu_type >= ACPI_APMT_NODE_TYPE_COUNT) {
+	switch (pmu_type) {
+	default:
 		dev_err(dev, "unsupported PMU type-%u\n", pmu_type);
 		return NULL;
-	}
-
-	if (pmu_type == ACPI_APMT_NODE_TYPE_ACPI) {
+	case ACPI_APMT_NODE_TYPE_ACPI:
 		memcpy(acpi_hid_string,
 			&apmt_node->inst_primary,
 			sizeof(apmt_node->inst_primary));
-		name = devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%s_%u", PMUNAME,
+		return devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%s_%u", PMUNAME,
 				      arm_cspmu_type_str[pmu_type],
 				      acpi_hid_string,
 				      apmt_node->inst_secondary);
-	} else {
-		name = devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%d", PMUNAME,
-				      arm_cspmu_type_str[pmu_type],
-				      atomic_fetch_inc(&pmu_idx[pmu_type]));
-	}
+	case ACPI_APMT_NODE_TYPE_MC:
+		id = apmt_node->id;
+		break;
+	case ACPI_APMT_NODE_TYPE_SMMU:
+	case ACPI_APMT_NODE_TYPE_PCIE_ROOT:
+		id = apmt_node->inst_primary;
+		break;
+	case ACPI_APMT_NODE_TYPE_CACHE:
+		id = apmt_node->inst_secondary;
+		break;
+	};
 
-	return name;
+	return devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%u", PMUNAME,
+			      arm_cspmu_type_str[pmu_type],
+			      apmt_node->id);
 }
 
 static ssize_t arm_cspmu_cpumask_show(struct device *dev,
-- 
2.54.0.dirty

[PATCH 3/4] perf/arm_cspmu: Improve sub-module error reporting

[Robin Murphy]

When waiting for a sub-module to register, we return a bare
-EPROBE_DEFER that ends up showing the end user:

  platform arm-cs-arch-pmu.1: deferred probe pending (no reason)

wherein it's not necessarily clear that they might need to take some
action to ensure the appropriate module is available to load. Let's use
dev_err_probe() here so we can show exactly what we're waiting for.

Similarly, in the case where something's gone horribly wrong with an
already-registered module, we can use dev_WARN() to standardise the
device/driver attribution rather than just open-coding "arm_cspmu".

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/perf/arm_cspmu/arm_cspmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
index 0570be74d11f..0b26a1588eba 100644
--- a/drivers/perf/arm_cspmu/arm_cspmu.c
+++ b/drivers/perf/arm_cspmu/arm_cspmu.c
@@ -438,13 +438,15 @@ static int arm_cspmu_init_impl_ops(struct arm_cspmu *cspmu)
 				if (ret)
 					module_put(match->module);
 			} else {
-				WARN(1, "arm_cspmu failed to get module: %s\n",
+				dev_WARN(cspmu->dev, "Failed to get module: %s\n",
 					match->module_name);
 				ret = -EINVAL;
 			}
 		} else {
 			request_module_nowait(match->module_name);
-			ret = -EPROBE_DEFER;
+			ret = dev_err_probe(cspmu->dev, -EPROBE_DEFER,
+					    "Waiting for module %s to load\n",
+					    match->module_name);
 		}
 
 		mutex_unlock(&arm_cspmu_lock);
-- 
2.54.0.dirty

[PATCH 4/4] perf/arm_cspmu: Make IRQ more optional

[Robin Murphy]

If we have 64-bit counters, we can reasonably assume we'll never have to
handle an overflow before the end of the universe (since we're a system
PMU with no sampling). Thus even if firmware does specify an IRQ, we can
still continue in the event of being unable to request it. This can help
systems where IRQs cannot be claimed exclusively, or are broken in other
ways.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/perf/arm_cspmu/arm_cspmu.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
index 0b26a1588eba..4ba47bccc99c 100644
--- a/drivers/perf/arm_cspmu/arm_cspmu.c
+++ b/drivers/perf/arm_cspmu/arm_cspmu.c
@@ -1257,8 +1257,11 @@ static int arm_cspmu_device_probe(struct platform_device *pdev)
 		return ret;
 
 	ret = arm_cspmu_request_irq(cspmu);
-	if (ret)
-		return ret;
+	if (ret) {
+		if (counter_size(cspmu) < 64)
+			return ret;
+		dev_info(cspmu->dev, "Continuing without IRQ\n");
+	}
 
 	ret = arm_cspmu_get_cpus(cspmu);
 	if (ret)
-- 
2.54.0.dirty

Re: [PATCH 1/4] ACPI/APMT: Use stable device ID

[Robin Murphy]

On 09/07/2026 3:39 pm, Robin Murphy wrote:
> The APMT node format includes a unique identifier, so we can use this as
> the platform device ID to give userspace stable and identifiable device
> names, rather than auto numbering dependent on how the table is parsed.
> 
> Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
> Cc: Hanjun Guo <guohanjun@huawei.com>
> Cc: Sudeep Holla <sudeep.holla@kernel.org>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>   drivers/acpi/arm64/apmt.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/arm64/apmt.c b/drivers/acpi/arm64/apmt.c
> index bb010f6164e5..ba48fcb26d52 100644
> --- a/drivers/acpi/arm64/apmt.c
> +++ b/drivers/acpi/arm64/apmt.c
> @@ -79,7 +79,7 @@ static int __init apmt_add_platform_device(struct acpi_apmt_node *node,
>   	int ret, count;
>   	struct resource res[DEV_MAX_RESOURCE_COUNT];
>   
> -	pdev = platform_device_alloc(DEV_NAME, PLATFORM_DEVID_AUTO);
> +	pdev = platform_device_alloc(DEV_NAME, node->id);

Per the Sashiko comment, while I really wouldn't expect it to be an 
issue in practice, I guess we could explicitly check and truncate 
node->id to INT_MAX (probably with some degree of warning) here just in 
case.

Cheers,
Robin.

>   	if (!pdev)
>   		return -ENOMEM;
>   

Re: [PATCH 2/4] perf/arm_cspmu: Improve APMT-based PMU naming

[Robin Murphy]

On 09/07/2026 3:39 pm, Robin Murphy wrote:
> On ACPI systems, it has not actually been possible for userspace to
> reliably tell which PMU corresponds to which APMT entry for types
> other than "ACPI device" - the evidence trail only leads from the
> arbitrarily-numbered PMU device to its arbitrarily-numbered parent
> platform device that has no distinguishing features either.
> 
> While we've now improved the platform device creation to associate the
> actual APMT unique ID, we may as well also tweak the PMU devices to
> substitute the arbitrary number with a different arbitrary number that
> might be more directly meaningful based on the APMT definitions.
> 
> We don't have an equivalent for Devicetree, but in that case the
> platform devices are at least identifiable via their sysfs-visible
> of_node.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>   drivers/perf/arm_cspmu/arm_cspmu.c | 36 +++++++++++++++++-------------
>   1 file changed, 21 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
> index 80fb314d5135..0570be74d11f 100644
> --- a/drivers/perf/arm_cspmu/arm_cspmu.c
> +++ b/drivers/perf/arm_cspmu/arm_cspmu.c
> @@ -250,38 +250,44 @@ static const char *arm_cspmu_get_name(const struct arm_cspmu *cspmu)
>   	struct device *dev;
>   	struct acpi_apmt_node *apmt_node;
>   	u8 pmu_type;
> -	char *name;
>   	char acpi_hid_string[ACPI_ID_LEN] = { 0 };
> -	static atomic_t pmu_idx[ACPI_APMT_NODE_TYPE_COUNT] = { 0 };
> +	static atomic_t pmu_idx;
> +	u32 id;
>   
>   	dev = cspmu->dev;
>   	apmt_node = arm_cspmu_apmt_node(dev);
>   	if (!apmt_node)
>   		return devm_kasprintf(dev, GFP_KERNEL, PMUNAME "_%u",
> -				      atomic_fetch_inc(&pmu_idx[0]));
> +				      atomic_fetch_inc(&pmu_idx));
>   
>   	pmu_type = apmt_node->type;
> -
> -	if (pmu_type >= ACPI_APMT_NODE_TYPE_COUNT) {
> +	switch (pmu_type) {
> +	default:
>   		dev_err(dev, "unsupported PMU type-%u\n", pmu_type);
>   		return NULL;
> -	}
> -
> -	if (pmu_type == ACPI_APMT_NODE_TYPE_ACPI) {
> +	case ACPI_APMT_NODE_TYPE_ACPI:
>   		memcpy(acpi_hid_string,
>   			&apmt_node->inst_primary,
>   			sizeof(apmt_node->inst_primary));
> -		name = devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%s_%u", PMUNAME,
> +		return devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%s_%u", PMUNAME,
>   				      arm_cspmu_type_str[pmu_type],
>   				      acpi_hid_string,
>   				      apmt_node->inst_secondary);
> -	} else {
> -		name = devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%d", PMUNAME,
> -				      arm_cspmu_type_str[pmu_type],
> -				      atomic_fetch_inc(&pmu_idx[pmu_type]));
> -	}
> +	case ACPI_APMT_NODE_TYPE_MC:
> +		id = apmt_node->id;
> +		break;
> +	case ACPI_APMT_NODE_TYPE_SMMU:
> +	case ACPI_APMT_NODE_TYPE_PCIE_ROOT:
> +		id = apmt_node->inst_primary;
> +		break;
> +	case ACPI_APMT_NODE_TYPE_CACHE:
> +		id = apmt_node->inst_secondary;
> +		break;
> +	};
>   
> -	return name;
> +	return devm_kasprintf(dev, GFP_KERNEL, "%s_%s_%u", PMUNAME,
> +			      arm_cspmu_type_str[pmu_type],
> +			      apmt_node->id);

Seems I did forget this when I realised the instance fields could be 
useful and added the local "id" variable. The rest of the Sashiko noise 
is mostly nonsense.

Cheers,
Robin.

>   }
>   
>   static ssize_t arm_cspmu_cpumask_show(struct device *dev,