linux-kernel - Re: [PATCH 4/5] cacheinfo: Expose the code to generate a cache-id from a device

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Message-ID: <20250617172132.00002844@huawei.com>
Date: Tue, 17 Jun 2025 17:21:32 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: James Morse <james.morse@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J . Wysocki"
	<rafael@...nel.org>, <sudeep.holla@....com>, Rob Herring <robh@...nel.org>,
	Ben Horgan <ben.horgan@....com>
Subject: Re: [PATCH 4/5] cacheinfo: Expose the code to generate a cache-id
 from a device_node

On Fri, 13 Jun 2025 13:03:55 +0000
James Morse <james.morse@....com> wrote:

> The MPAM driver identifies caches by id for use with resctrl. It
> needs to know the cache-id when probe-ing, but the value isn't set
> in cacheinfo until the corresponding CPU comes online.
> 
> Expose the code that generates the cache-id. This allows the MPAM
> driver to determine the properties of the caches without waiting
> for all CPUs to come online.
> 
> Signed-off-by: James Morse <james.morse@....com>
Feels to me like this needs to come with the user.
The earlier patches at least expose it via existing infrastructure
this isn't used at all yet...

> ---
>  drivers/base/cacheinfo.c  | 15 +++++++++++----
>  include/linux/cacheinfo.h |  1 +
>  2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index d8e5b4c7156c..6316d80abab8 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -188,7 +188,7 @@ static bool cache_node_is_unified(struct cacheinfo *this_leaf,
>  #define arch_compact_of_hwid(_x)	(_x)
>  #endif
>  
> -static void cache_of_set_id(struct cacheinfo *this_leaf, struct device_node *np)
> +unsigned long cache_of_get_id(struct device_node *np)
Bit confusing to have cache_of_set_id() call cache_of_get_id() like this because
they are in no way mirrors of each other.   Rename?
(and naturally I'm providing no suggestions :)

>  {
>  	struct device_node *cpu;
>  	u32 min_id = ~0;
> @@ -200,7 +200,7 @@ static void cache_of_set_id(struct cacheinfo *this_leaf, struct device_node *np)
>  		id = arch_compact_of_hwid(id);
>  		if (FIELD_GET(GENMASK_ULL(63, 32), id)) {
>  			of_node_put(cpu);
> -			return;
> +			return ~0UL;
>  		}
>  		while (1) {
>  			if (!cache_node)
> @@ -214,8 +214,15 @@ static void cache_of_set_id(struct cacheinfo *this_leaf, struct device_node *np)
>  		}
>  	}
>  
> -	if (min_id != ~0) {
> -		this_leaf->id = min_id;
> +	return min_id;
> +}
> +
> +static void cache_of_set_id(struct cacheinfo *this_leaf, struct device_node *np)
> +{
> +	unsigned long id = cache_of_get_id(np);
> +
> +	if (id != ~0UL) {
> +		this_leaf->id = id;
>  		this_leaf->attributes |= CACHE_ID;
>  	}
>  }
> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
> index c8f4f0a0b874..9c959caf8af8 100644
> --- a/include/linux/cacheinfo.h
> +++ b/include/linux/cacheinfo.h
> @@ -112,6 +112,7 @@ int acpi_get_cache_info(unsigned int cpu,
>  #endif
>  
>  const struct attribute_group *cache_get_priv_group(struct cacheinfo *this_leaf);
> +unsigned long cache_of_get_id(struct device_node *np);
>  
>  /*
>   * Get the cacheinfo structure for the cache associated with @cpu at