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

James Morse posted 36 patches 2 months, 3 weeks ago
There is a newer version of this series
[RFC PATCH 04/36] cacheinfo: Expose the code to generate a cache-id from a device_node
Posted by James Morse 2 months, 3 weeks ago 
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;
+}
+
+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
-- 
2.39.5
Re: [RFC PATCH 04/36] cacheinfo: Expose the code to generate a cache-id from a device_node
Posted by Ben Horgan 2 months, 3 weeks ago 
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
Re: [RFC PATCH 04/36] cacheinfo: Expose the code to generate a cache-id from a device_node
Posted by James Morse 2 months, 1 week ago 
Hi Ben,

On 14/07/2025 12:40, Ben Horgan wrote:
> 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().

>> 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?

Certainly some confusion - yup, because cache_of_calculate_id() needs to return something
that is out of range and (u32)-1 might be valid...

I think changing min_id to be defined as:
|	unsigned long min_id = ~0UL;

fixes this - any trip round the loop that doesn't match anything will eventually return ~0UL.


Thanks! - I always get the 'UL' suffixes wrong.

James
Re: [RFC PATCH 04/36] cacheinfo: Expose the code to generate a cache-id from a device_node
Posted by Ben Horgan 2 months, 1 week ago 
Hi James,

On 7/25/25 18:08, James Morse wrote:
> Hi Ben,
> 
> On 14/07/2025 12:40, Ben Horgan wrote:
>> 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().
> 
>>> 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?
> 
> Certainly some confusion - yup, because cache_of_calculate_id() needs to return something
> that is out of range and (u32)-1 might be valid...
> 
> I think changing min_id to be defined as:
> |	unsigned long min_id = ~0UL;
> 
> fixes this - any trip round the loop that doesn't match anything will eventually return ~0UL.
Yes, that would work.

> 
> 
> Thanks! - I always get the 'UL' suffixes wrong.
> 
> James

Thanks,

Ben

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