Subject: Re: [PATCH v2 3/8] perf/arm_cspmu: Add arm_cspmu_acpi_dev_get

From: Jonathan Cameron <[email-masked]>
Date: Thu, 19 Feb 2026 09:40:21 +0000

On Wed, 18 Feb 2026 14:58:04 +0000
Besar Wicaksono <[email-masked]> wrote:

> Add interface to get ACPI device associated with the
> PMU. This ACPI device may contain additional properties
> not covered by the standard properties.
> 
> Reviewed-by: Ilkka Koskinen <[email-masked]>
> Signed-off-by: Besar Wicaksono <[email-masked]>
Hi Besar,

A drive by review as I was curious.

A few comments inline.
> ---
>  drivers/perf/arm_cspmu/arm_cspmu.c | 22 +++++++++++++++++++++-
>  drivers/perf/arm_cspmu/arm_cspmu.h | 17 ++++++++++++++++-
>  2 files changed, 37 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
> index 34430b68f602..ab2479c048bb 100644
> --- a/drivers/perf/arm_cspmu/arm_cspmu.c
> +++ b/drivers/perf/arm_cspmu/arm_cspmu.c
> @@ -16,7 +16,7 @@
>   * The user should refer to the vendor technical documentation to get details
>   * about the supported events.
>   *
> - * Copyright (c) 2022-2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
> + * Copyright (c) 2022-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
>   *
>   */
>  
> @@ -1132,6 +1132,26 @@ static int arm_cspmu_acpi_get_cpus(struct arm_cspmu *cspmu)
>  
>  	return 0;
>  }
> +
> +struct acpi_device *arm_cspmu_acpi_dev_get(const struct arm_cspmu *cspmu)
> +{
> +	char hid[16];
> +	char uid[16];

Might as well do
	char hid[16] = { };
	char uid[16] = { };

and drop the memsets below.

> +	const struct acpi_apmt_node *apmt_node;
> +
> +	apmt_node = arm_cspmu_apmt_node(cspmu->dev);
> +	if (!apmt_node || apmt_node->type != ACPI_APMT_NODE_TYPE_ACPI)
> +		return NULL;
> +
> +	memset(hid, 0, sizeof(hid));
> +	memset(uid, 0, sizeof(uid));
> +
> +	memcpy(hid, &apmt_node->inst_primary, sizeof(apmt_node->inst_primary));
> +	snprintf(uid, sizeof(uid), "%u", apmt_node->inst_secondary);
> +
> +	return acpi_dev_get_first_match_dev(hid, uid, -1);
> +}
> +EXPORT_SYMBOL_GPL(arm_cspmu_acpi_dev_get);
>  #else
>  static int arm_cspmu_acpi_get_cpus(struct arm_cspmu *cspmu)
>  {
> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.h b/drivers/perf/arm_cspmu/arm_cspmu.h
> index cd65a58dbd88..320096673200 100644
> --- a/drivers/perf/arm_cspmu/arm_cspmu.h
> +++ b/drivers/perf/arm_cspmu/arm_cspmu.h
> @@ -1,13 +1,14 @@
>  /* SPDX-License-Identifier: GPL-2.0
>   *
>   * ARM CoreSight Architecture PMU driver.
> - * Copyright (c) 2022-2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
> + * Copyright (c) 2022-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
>   *
>   */
>  
>  #ifndef __ARM_CSPMU_H__
>  #define __ARM_CSPMU_H__
>  
> +#include <linux/acpi.h>
>  #include <linux/bitfield.h>
>  #include <linux/cpumask.h>
>  #include <linux/device.h>
> @@ -255,4 +256,18 @@ int arm_cspmu_impl_register(const struct arm_cspmu_impl_match *impl_match);
>  /* Unregister vendor backend. */
>  void arm_cspmu_impl_unregister(const struct arm_cspmu_impl_match *impl_match);
>  
> +#if defined(CONFIG_ACPI)
This isn't the same gate as used for whether the function is built. I think that's 
#if defined(CONFIG_ACPI) && defined(CONFIG_ARM64)

Whilst it might work to have them different today I think this is a little more
fragile than would be ideal.

The ARM64 bit seems to be there to allow COMPILE_TEST for
ARM_CORESIGHT_PMU_ARCH_SYSTEM_PMU  and to me that smells like a stub or Kconfig
dependency missing.

> +/**
> + * Get ACPI device associated with the PMU.
> + * The caller is responsible for calling acpi_dev_put() on the returned device.
> + */
> +struct acpi_device *arm_cspmu_acpi_dev_get(const struct arm_cspmu *cspmu);
> +#else
> +static inline struct acpi_device *
> +arm_cspmu_acpi_dev_get(const struct arm_cspmu *cspmu)
> +{
> +	return NULL;
> +}
> +#endif
> +
>  #endif /* __ARM_CSPMU_H__ */