Re: [RFC PATCH 04/36] cacheinfo: Expose the code to generate a cache-id from a device_node

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

Hi James,

On 7/11/25 19:36, James Morse 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 device_initcall().
> 
> Expose the code that generates the cache-id. The parts of the MPAM
> driver that run early can use this to set up the resctrl structures
> before cacheinfo is ready in device_initcall().
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
>   * Renamed cache_of_get_id() cache_of_calculate_id().
> ---
>   drivers/base/cacheinfo.c  | 17 ++++++++++++-----
>   include/linux/cacheinfo.h |  1 +
>   2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index 613410705a47..0fdd6358ee73 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -207,8 +207,7 @@ static bool match_cache_node(struct device_node *cpu,
>   #define arch_compact_of_hwid(_x)	(_x)
>   #endif
>   
> -static void cache_of_set_id(struct cacheinfo *this_leaf,
> -			    struct device_node *cache_node)
> +unsigned long cache_of_calculate_id(struct device_node *cache_node)
>   {
>   	struct device_node *cpu;
>   	u32 min_id = ~0;
> @@ -219,15 +218,23 @@ static void cache_of_set_id(struct cacheinfo *this_leaf,
>   		id = arch_compact_of_hwid(id);
>   		if (FIELD_GET(GENMASK_ULL(63, 32), id)) {
>   			of_node_put(cpu);
> -			return;
> +			return ~0UL;
>   		}
>   
>   		if (match_cache_node(cpu, cache_node))
>   			min_id = min(min_id, id);
>   	}
>   
> -	if (min_id != ~0) {
> -		this_leaf->id = min_id;
> +	return min_id;
Looks like some 32bit/64bit confusion. Don't we want to return ~0UL if 
min_id == ~0?
> +}
> +
> +static void cache_of_set_id(struct cacheinfo *this_leaf,
> +			    struct device_node *cache_node)
> +{
> +	unsigned long id = cache_of_calculate_id(cache_node);
> +
> +	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..2dcbb69139e9 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_calculate_id(struct device_node *np);
>   
>   /*
>    * Get the cacheinfo structure for the cache associated with @cpu at

Thanks,

Ben