linux-kernel - Re: [PATCH v3 06/29] ACPI / MPAM: Parse the MPAM table

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Message-ID: <b0369cf6-229d-458b-9f42-a78e4cf3be94@arm.com>
Date: Mon, 20 Oct 2025 13:29:10 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 fenghuay@...dia.com, baisheng.gao@...soc.com,
 Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring
 <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>, Jeremy Linton <jeremy.linton@....com>,
 Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 06/29] ACPI / MPAM: Parse the MPAM table

Hi James,

On 10/17/25 19:56, 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.
> 
> This happens in two stages. Platform devices are created first for the
> MSC devices. Once the driver probes it calls acpi_mpam_parse_resources()
> to discover the RIS entries the MSC contains.
> 
> For now the MPAM hook mpam_ris_create() is stubbed out, but will update
> the MPAM driver with optional discovered data about the RIS entries.
> 
> CC: Carl Worth <carl@...amperecomputing.com>
> Link: https://developer.arm.com/documentation/den0065/3-0bet/?lang=en
> Reviewed-by: Lorenzo Pieralisi <lpieralisi@...nel.org>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> Signed-off-by: James Morse <james.morse@....com>
> 
> ---
> Changes since v2:
>  * Expanded commit message.
>  * Moved explicit memset() to array initialisation.
>  * Added comments on the sizing of arrays.
>  * Moved MSC table entry parsing to a helper to allow use of a platform-device
>    cleanup rune, result int more returns and fewer breaks.
>  * Changed pre-processor macros for table bits.
>  * Discover unsupported PPI partitions purely from the table to make gicv5
>    easier, which also simplifies acpi_mpam_parse_irqs()
>  * Gave interface type numbers pre-processor names.
>  * Clarified some comments.
>  * Fixed the WARN_ON comparison in acpi_mpam_parse_msc().
>  * Made buffer over-run noisier.
>  * Print an error condition as %d not %u.
>  * Print a debug message when bad NUMA nodes are found.
> 
[...]
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index a9dbacabdf89..9d66421f68ff 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -8,6 +8,7 @@
>  #ifndef _LINUX_ACPI_H
>  #define _LINUX_ACPI_H
>  
> +#include <linux/cleanup.h>
>  #include <linux/errno.h>
>  #include <linux/ioport.h>	/* for struct resource */
>  #include <linux/resource_ext.h>
> @@ -221,6 +222,17 @@ void acpi_reserve_initial_tables (void);
>  void acpi_table_init_complete (void);
>  int acpi_table_init (void);
>  
> +static inline struct acpi_table_header *acpi_get_table_ret(char *signature, u32 instance)
> +{
> +	struct acpi_table_header *table;
> +	int status = acpi_get_table(signature, instance, &table);
> +
> +	if (ACPI_FAILURE(status))
> +		return ERR_PTR(-ENOENT);
> +	return table;
> +}
> +DEFINE_FREE(acpi_table, struct acpi_table_header *, if (!IS_ERR(_T)) acpi_put_table(_T))

Any reason to not change this to !IS_ERR_OR_NULL(_T) as Jonathan
suggested in his v2 review.

> +
>  int acpi_table_parse(char *id, acpi_tbl_table_handler handler);
>  int __init_or_acpilib acpi_table_parse_entries(char *id,
>  		unsigned long table_size, int entry_id,
> diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
> new file mode 100644
> index 000000000000..3d6c39c667c3
> --- /dev/null
> +++ b/include/linux/arm_mpam.h
> @@ -0,0 +1,48 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2025 Arm Ltd. */
> +
> +#ifndef __LINUX_ARM_MPAM_H
> +#define __LINUX_ARM_MPAM_H
> +
> +#include <linux/acpi.h>
> +#include <linux/types.h>
> +
> +#define GLOBAL_AFFINITY		~0
> +
> +struct mpam_msc;
> +
> +enum mpam_msc_iface {
> +	MPAM_IFACE_MMIO,	/* a real MPAM MSC */
> +	MPAM_IFACE_PCC,		/* a fake MPAM MSC */
> +};
> +
> +enum mpam_class_types {
> +	MPAM_CLASS_CACHE,       /* Well known caches, e.g. L2 */
> +	MPAM_CLASS_MEMORY,      /* Main memory */
> +	MPAM_CLASS_UNKNOWN,     /* Everything else, e.g. SMMU */
> +};
> +
> +#ifdef CONFIG_ACPI_MPAM
> +/* Parse the ACPI description of resources entries for this MSC. */
> +int acpi_mpam_parse_resources(struct mpam_msc *msc,
> +			      struct acpi_mpam_msc_node *tbl_msc);
> +
> +int acpi_mpam_count_msc(void);
> +#else
> +static inline int acpi_mpam_parse_resources(struct mpam_msc *msc,
> +					    struct acpi_mpam_msc_node *tbl_msc)
> +{
> +	return -EINVAL;
> +}
> +
> +static inline int acpi_mpam_count_msc(void) { return -EINVAL; }
> +#endif
> +
> +static inline int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
> +				  enum mpam_class_types type, u8 class_id,
> +				  int component_id)
> +{
> +	return -EINVAL;
> +}
> +
> +#endif /* __LINUX_ARM_MPAM_H */
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index 074754c23d33..23a30ada2d4c 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -232,6 +232,7 @@ extern int platform_device_add_data(struct platform_device *pdev,
>  extern int platform_device_add(struct platform_device *pdev);
>  extern void platform_device_del(struct platform_device *pdev);
>  extern void platform_device_put(struct platform_device *pdev);
> +DEFINE_FREE(platform_device_put, struct platform_device *, if (_T) platform_device_put(_T))

Significant enough to be mentioned in the commit message?

This DEFINE_FREE is named after the free-ing function,
platform_device_put, whereas the previous DEFINE_FREE in this patch is
named after the struct, acpi_table. On grepping I see both naming
schemes - not sure if there is a recommendation for new code.

>  
>  struct platform_driver {
>  	int (*probe)(struct platform_device *);

Thanks,

Ben