The MPAM table identifies caches by id. The MPAM driver also wants to know
the cache level to determine if the platform is of the shape that can be
managed via resctrl. Cacheinfo has this information, but only for CPUs that
are online.
Waiting for all CPUs to come online is a problem for platforms where
CPUs are brought online late by user-space.
Add a helper that walks every possible cache, until it finds the one
identified by cache-id, then return the level.
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v1:
* Droppeed the cleanup based table freeing, use acpi_get_pptt() instead.
* Removed a confusing comment.
* Clarified the kernel doc.
Changes since RFC:
* acpi_count_levels() now returns a value.
* Converted the table-get stuff to use Jonathan's cleanup helper.
* Dropped Sudeep's Review tag due to the cleanup change.
---
drivers/acpi/pptt.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/acpi.h | 5 ++++
2 files changed, 67 insertions(+)
diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index 7af7d62597df..c5f2a51d280b 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -904,3 +904,65 @@ void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
entry->length);
}
}
+
+/*
+ * find_acpi_cache_level_from_id() - Get the level of the specified cache
+ * @cache_id: The id field of the unified cache
+ *
+ * Determine the level relative to any CPU for the unified cache identified by
+ * cache_id. This allows the property to be found even if the CPUs are offline.
+ *
+ * The returned level can be used to group unified caches that are peers.
+ *
+ * The PPTT table must be rev 3 or later,
+ *
+ * If one CPUs L2 is shared with another as L3, this function will return
+ * an unpredictable value.
+ *
+ * Return: -ENOENT if the PPTT doesn't exist, the revision isn't supported or
+ * the cache cannot be found.
+ * Otherwise returns a value which represents the level of the specified cache.
+ */
+int find_acpi_cache_level_from_id(u32 cache_id)
+{
+ u32 acpi_cpu_id;
+ int level, cpu, num_levels;
+ struct acpi_pptt_cache *cache;
+ struct acpi_table_header *table;
+ struct acpi_pptt_cache_v1 *cache_v1;
+ struct acpi_pptt_processor *cpu_node;
+
+ table = acpi_get_pptt();
+ if (!table)
+ return -ENOENT;
+
+ if (table->revision < 3)
+ return -ENOENT;
+
+ for_each_possible_cpu(cpu) {
+ acpi_cpu_id = get_acpi_id_for_cpu(cpu);
+ cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
+ if (!cpu_node)
+ return -ENOENT;
+ num_levels = acpi_count_levels(table, cpu_node, NULL);
+
+ /* Start at 1 for L1 */
+ for (level = 1; level <= num_levels; level++) {
+ cache = acpi_find_cache_node(table, acpi_cpu_id,
+ ACPI_PPTT_CACHE_TYPE_UNIFIED,
+ level, &cpu_node);
+ if (!cache)
+ continue;
+
+ cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
+ cache,
+ sizeof(struct acpi_pptt_cache));
+
+ if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
+ cache_v1->cache_id == cache_id)
+ return level;
+ }
+ }
+
+ return -ENOENT;
+}
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index f97a9ff678cc..5bdca5546697 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1542,6 +1542,7 @@ int find_acpi_cpu_topology_cluster(unsigned int cpu);
int find_acpi_cpu_topology_package(unsigned int cpu);
int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
+int find_acpi_cache_level_from_id(u32 cache_id);
#else
static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
{
@@ -1565,6 +1566,10 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
}
static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
cpumask_t *cpus) { }
+static inline int find_acpi_cache_level_from_id(u32 cache_id)
+{
+ return -EINVAL;
+}
#endif
void acpi_arch_init(void);
--
2.39.5
On 9/10/25 13:42, James Morse wrote:
> The MPAM table identifies caches by id. The MPAM driver also wants to know
> the cache level to determine if the platform is of the shape that can be
> managed via resctrl. Cacheinfo has this information, but only for CPUs that
> are online.
>
> Waiting for all CPUs to come online is a problem for platforms where
> CPUs are brought online late by user-space.
>
> Add a helper that walks every possible cache, until it finds the one
> identified by cache-id, then return the level.
>
> Signed-off-by: James Morse <james.morse@arm.com>
Other than minor comment issues as follows,
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
> ---
> Changes since v1:
> * Droppeed the cleanup based table freeing, use acpi_get_pptt() instead.
> * Removed a confusing comment.
> * Clarified the kernel doc.
>
> Changes since RFC:
> * acpi_count_levels() now returns a value.
> * Converted the table-get stuff to use Jonathan's cleanup helper.
> * Dropped Sudeep's Review tag due to the cleanup change.
> ---
> drivers/acpi/pptt.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 5 ++++
> 2 files changed, 67 insertions(+)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 7af7d62597df..c5f2a51d280b 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -904,3 +904,65 @@ void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
> entry->length);
> }
> }
> +
> +/*
> + * find_acpi_cache_level_from_id() - Get the level of the specified cache
> + * @cache_id: The id field of the unified cache
> + *
> + * Determine the level relative to any CPU for the unified cache identified by
> + * cache_id. This allows the property to be found even if the CPUs are offline.
> + *
> + * The returned level can be used to group unified caches that are peers.
> + *
> + * The PPTT table must be rev 3 or later,
s/,/./
> + *
> + * If one CPUs L2 is shared with another as L3, this function will return
This comment is not clear. Maybe it's better to say:
+ * If one CPU's L2 is shared with another CPU as L3, this function will
return
> + * an unpredictable value.
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, the revision isn't supported or
> + * the cache cannot be found.
> + * Otherwise returns a value which represents the level of the specified cache.
> + */
> +int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + u32 acpi_cpu_id;
> + int level, cpu, num_levels;
> + struct acpi_pptt_cache *cache;
> + struct acpi_table_header *table;
> + struct acpi_pptt_cache_v1 *cache_v1;
> + struct acpi_pptt_processor *cpu_node;
> +
> + table = acpi_get_pptt();
> + if (!table)
> + return -ENOENT;
> +
> + if (table->revision < 3)
> + return -ENOENT;
> +
> + for_each_possible_cpu(cpu) {
> + acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> + cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
> + if (!cpu_node)
> + return -ENOENT;
> + num_levels = acpi_count_levels(table, cpu_node, NULL);
> +
> + /* Start at 1 for L1 */
> + for (level = 1; level <= num_levels; level++) {
> + cache = acpi_find_cache_node(table, acpi_cpu_id,
> + ACPI_PPTT_CACHE_TYPE_UNIFIED,
> + level, &cpu_node);
> + if (!cache)
> + continue;
> +
> + cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
> + cache,
> + sizeof(struct acpi_pptt_cache));
> +
> + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
> + cache_v1->cache_id == cache_id)
> + return level;
> + }
> + }
> +
> + return -ENOENT;
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index f97a9ff678cc..5bdca5546697 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1542,6 +1542,7 @@ int find_acpi_cpu_topology_cluster(unsigned int cpu);
> int find_acpi_cpu_topology_package(unsigned int cpu);
> int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
> void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
> +int find_acpi_cache_level_from_id(u32 cache_id);
> #else
> static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
> {
> @@ -1565,6 +1566,10 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> }
> static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
> cpumask_t *cpus) { }
> +static inline int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + return -EINVAL;
> +}
> #endif
>
> void acpi_arch_init(void);
Thanks.
-Fenghua
On Wed, Sep 10, 2025 at 08:42:43PM +0000, James Morse wrote:
> The MPAM table identifies caches by id. The MPAM driver also wants to know
> the cache level to determine if the platform is of the shape that can be
> managed via resctrl. Cacheinfo has this information, but only for CPUs that
> are online.
>
> Waiting for all CPUs to come online is a problem for platforms where
> CPUs are brought online late by user-space.
>
> Add a helper that walks every possible cache, until it finds the one
> identified by cache-id, then return the level.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
> * Droppeed the cleanup based table freeing, use acpi_get_pptt() instead.
> * Removed a confusing comment.
> * Clarified the kernel doc.
>
> Changes since RFC:
> * acpi_count_levels() now returns a value.
> * Converted the table-get stuff to use Jonathan's cleanup helper.
> * Dropped Sudeep's Review tag due to the cleanup change.
> ---
> drivers/acpi/pptt.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 5 ++++
> 2 files changed, 67 insertions(+)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 7af7d62597df..c5f2a51d280b 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -904,3 +904,65 @@ void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
> entry->length);
> }
> }
> +
> +/*
> + * find_acpi_cache_level_from_id() - Get the level of the specified cache
> + * @cache_id: The id field of the unified cache
> + *
> + * Determine the level relative to any CPU for the unified cache identified by
> + * cache_id. This allows the property to be found even if the CPUs are offline.
> + *
> + * The returned level can be used to group unified caches that are peers.
> + *
> + * The PPTT table must be rev 3 or later,
* The PPTT table must be rev 3 or later.
> + *
> + * If one CPUs L2 is shared with another as L3, this function will return
> + * an unpredictable value.
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, the revision isn't supported or
> + * the cache cannot be found.
> + * Otherwise returns a value which represents the level of the specified cache.
> + */
> +int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + u32 acpi_cpu_id;
> + int level, cpu, num_levels;
> + struct acpi_pptt_cache *cache;
> + struct acpi_table_header *table;
> + struct acpi_pptt_cache_v1 *cache_v1;
> + struct acpi_pptt_processor *cpu_node;
> +
> + table = acpi_get_pptt();
> + if (!table)
> + return -ENOENT;
> +
> + if (table->revision < 3)
> + return -ENOENT;
> +
> + for_each_possible_cpu(cpu) {
> + acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> + cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
> + if (!cpu_node)
> + return -ENOENT;
Same comment as in another patch - don't think you want to stop parsing
here.
> + num_levels = acpi_count_levels(table, cpu_node, NULL);
> +
> + /* Start at 1 for L1 */
> + for (level = 1; level <= num_levels; level++) {
> + cache = acpi_find_cache_node(table, acpi_cpu_id,
> + ACPI_PPTT_CACHE_TYPE_UNIFIED,
> + level, &cpu_node);
> + if (!cache)
> + continue;
> +
> + cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
> + cache,
> + sizeof(struct acpi_pptt_cache));
> +
> + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
> + cache_v1->cache_id == cache_id)
> + return level;
> + }
> + }
> +
> + return -ENOENT;
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index f97a9ff678cc..5bdca5546697 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1542,6 +1542,7 @@ int find_acpi_cpu_topology_cluster(unsigned int cpu);
> int find_acpi_cpu_topology_package(unsigned int cpu);
> int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
> void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
> +int find_acpi_cache_level_from_id(u32 cache_id);
> #else
> static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
> {
> @@ -1565,6 +1566,10 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> }
> static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
> cpumask_t *cpus) { }
> +static inline int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + return -EINVAL;
return -ENOENT;
Reviewed-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
> +}
> #endif
>
> void acpi_arch_init(void);
> --
> 2.39.5
>
Hi Lorenzo,
On 11/09/2025 16:27, Lorenzo Pieralisi wrote:
> On Wed, Sep 10, 2025 at 08:42:43PM +0000, James Morse wrote:
>> The MPAM table identifies caches by id. The MPAM driver also wants to know
>> the cache level to determine if the platform is of the shape that can be
>> managed via resctrl. Cacheinfo has this information, but only for CPUs that
>> are online.
>>
>> Waiting for all CPUs to come online is a problem for platforms where
>> CPUs are brought online late by user-space.
>>
>> Add a helper that walks every possible cache, until it finds the one
>> identified by cache-id, then return the level.
>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>> index 7af7d62597df..c5f2a51d280b 100644
>> --- a/drivers/acpi/pptt.c
>> +++ b/drivers/acpi/pptt.c
>> @@ -904,3 +904,65 @@ void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
>> entry->length);
>> }
>> }
>> +
>> +/*
>> + * find_acpi_cache_level_from_id() - Get the level of the specified cache
>> + * @cache_id: The id field of the unified cache
>> + *
>> + * Determine the level relative to any CPU for the unified cache identified by
>> + * cache_id. This allows the property to be found even if the CPUs are offline.
>> + *
>> + * The returned level can be used to group unified caches that are peers.
>> + *
>> + * The PPTT table must be rev 3 or later,
>
> * The PPTT table must be rev 3 or later.
Fixed,
>> + *
>> + * If one CPUs L2 is shared with another as L3, this function will return
>> + * an unpredictable value.
>> + *
>> + * Return: -ENOENT if the PPTT doesn't exist, the revision isn't supported or
>> + * the cache cannot be found.
>> + * Otherwise returns a value which represents the level of the specified cache.
>> + */
>> +int find_acpi_cache_level_from_id(u32 cache_id)
>> +{
>> + u32 acpi_cpu_id;
>> + int level, cpu, num_levels;
>> + struct acpi_pptt_cache *cache;
>> + struct acpi_table_header *table;
>> + struct acpi_pptt_cache_v1 *cache_v1;
>> + struct acpi_pptt_processor *cpu_node;
>> +
>> + table = acpi_get_pptt();
>> + if (!table)
>> + return -ENOENT;
>> +
>> + if (table->revision < 3)
>> + return -ENOENT;
>> +
>> + for_each_possible_cpu(cpu) {
>> + acpi_cpu_id = get_acpi_id_for_cpu(cpu);
>> + cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
>> + if (!cpu_node)
>> + return -ENOENT;
>
> Same comment as in another patch - don't think you want to stop parsing
> here.
Yes - this is me throwing my hands up in the air at a nonsense firmware table.
'continue' would be a try harder approach.
>> + num_levels = acpi_count_levels(table, cpu_node, NULL);
>> +
>> + /* Start at 1 for L1 */
>> + for (level = 1; level <= num_levels; level++) {
>> + cache = acpi_find_cache_node(table, acpi_cpu_id,
>> + ACPI_PPTT_CACHE_TYPE_UNIFIED,
>> + level, &cpu_node);
>> + if (!cache)
>> + continue;
>> +
>> + cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
>> + cache,
>> + sizeof(struct acpi_pptt_cache));
>> +
>> + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
>> + cache_v1->cache_id == cache_id)
>> + return level;
>> + }
>> + }
>> +
>> + return -ENOENT;
>> +}
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index f97a9ff678cc..5bdca5546697 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -1565,6 +1566,10 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
>> }
>> static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
>> cpumask_t *cpus) { }
>> +static inline int find_acpi_cache_level_from_id(u32 cache_id)
>> +{
>> + return -EINVAL;
> return -ENOENT;
Yes, same bug as before. Fixed.
> Reviewed-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Thanks - I think the change to ignoring unified caches and searching all types is
substantive enough that I won't pick this up because of the changes for v3...
Thanks,
James
On Wed, 10 Sep 2025 20:42:43 +0000
James Morse <james.morse@arm.com> wrote:
> The MPAM table identifies caches by id. The MPAM driver also wants to know
> the cache level to determine if the platform is of the shape that can be
> managed via resctrl. Cacheinfo has this information, but only for CPUs that
> are online.
>
> Waiting for all CPUs to come online is a problem for platforms where
> CPUs are brought online late by user-space.
>
> Add a helper that walks every possible cache, until it finds the one
> identified by cache-id, then return the level.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
> * Droppeed the cleanup based table freeing, use acpi_get_pptt() instead.
> * Removed a confusing comment.
> * Clarified the kernel doc.
>
> Changes since RFC:
> * acpi_count_levels() now returns a value.
> * Converted the table-get stuff to use Jonathan's cleanup helper.
> * Dropped Sudeep's Review tag due to the cleanup change.
> ---
> drivers/acpi/pptt.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 5 ++++
> 2 files changed, 67 insertions(+)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 7af7d62597df..c5f2a51d280b 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -904,3 +904,65 @@ void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
> entry->length);
> }
> }
> +
> +/*
/**
It's an exposed interface so nice to have formal kernel-doc and automatic
checks that brings.
> + * find_acpi_cache_level_from_id() - Get the level of the specified cache
> + * @cache_id: The id field of the unified cache
> + *
> + * Determine the level relative to any CPU for the unified cache identified by
> + * cache_id. This allows the property to be found even if the CPUs are offline.
> + *
> + * The returned level can be used to group unified caches that are peers.
Silly question but why do we care if this a unified cache?
It's a bit odd to have a general sounding function fail for split caches.
The handling would have to be more complex but if we really don't want
to do it maybe rename the function to find_acpi_unifiedcache_level_from_id()
and if the general version gets added later we can switch to that.
> + *
> + * The PPTT table must be rev 3 or later,
> + *
> + * If one CPUs L2 is shared with another as L3, this function will return
> + * an unpredictable value.
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, the revision isn't supported or
> + * the cache cannot be found.
> + * Otherwise returns a value which represents the level of the specified cache.
> + */
> +int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + u32 acpi_cpu_id;
> + int level, cpu, num_levels;
> + struct acpi_pptt_cache *cache;
> + struct acpi_table_header *table;
> + struct acpi_pptt_cache_v1 *cache_v1;
> + struct acpi_pptt_processor *cpu_node;
> +
> + table = acpi_get_pptt();
> + if (!table)
> + return -ENOENT;
> +
> + if (table->revision < 3)
> + return -ENOENT;
> +
> + for_each_possible_cpu(cpu) {
> + acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> + cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
> + if (!cpu_node)
> + return -ENOENT;
> + num_levels = acpi_count_levels(table, cpu_node, NULL);
> +
> + /* Start at 1 for L1 */
> + for (level = 1; level <= num_levels; level++) {
> + cache = acpi_find_cache_node(table, acpi_cpu_id,
> + ACPI_PPTT_CACHE_TYPE_UNIFIED,
> + level, &cpu_node);
> + if (!cache)
> + continue;
> +
> + cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
> + cache,
> + sizeof(struct acpi_pptt_cache));
sizeof(*cache) to me makes this more obvious.
> +
> + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
> + cache_v1->cache_id == cache_id)
> + return level;
> + }
> + }
> +
> + return -ENOENT;
> +}
Hi Jonathan,
On 11/09/2025 11:59, Jonathan Cameron wrote:
> On Wed, 10 Sep 2025 20:42:43 +0000
> James Morse <james.morse@arm.com> wrote:
>
>> The MPAM table identifies caches by id. The MPAM driver also wants to know
>> the cache level to determine if the platform is of the shape that can be
>> managed via resctrl. Cacheinfo has this information, but only for CPUs that
>> are online.
>>
>> Waiting for all CPUs to come online is a problem for platforms where
>> CPUs are brought online late by user-space.
>>
>> Add a helper that walks every possible cache, until it finds the one
>> identified by cache-id, then return the level.
>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>> index 7af7d62597df..c5f2a51d280b 100644
>> --- a/drivers/acpi/pptt.c
>> +++ b/drivers/acpi/pptt.c
>> @@ -904,3 +904,65 @@ void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
>> entry->length);
>> }
>> }
>> +
>> +/*
> /**
>
> It's an exposed interface so nice to have formal kernel-doc and automatic
> checks that brings.
>
>> + * find_acpi_cache_level_from_id() - Get the level of the specified cache
>> + * @cache_id: The id field of the unified cache
>> + *
>> + * Determine the level relative to any CPU for the unified cache identified by
>> + * cache_id. This allows the property to be found even if the CPUs are offline.
>> + *
>> + * The returned level can be used to group unified caches that are peers.
> Silly question but why do we care if this a unified cache?
/me returns from the time-machine trip....
This is legacy, but results in parity with the DT approach.
Really early versions of this generated an ID based on the associated CPUs - like DT
does/would-do today. This value isn't unique for non-unified caches as they have the same
set of CPUs below them, so every use of cache-id used to have to check it was a unified cache.
This isn't a problem for MPAM as there is never likely to be an L1 MSC, but you're right-
it hinders re-use of this.
Since ACPI then went and added the ID to the PPTT, we don't need to check this here.
> It's a bit odd to have a general sounding function fail for split caches.
> The handling would have to be more complex but if we really don't want
> to do it maybe rename the function to find_acpi_unifiedcache_level_from_id()
> and if the general version gets added later we can switch to that.
I'll add the extra work - this avoids the call to acpi_count_levels() which was annoying
Dave as its another walk of the whole table. (I didn't twig in that conversation that the
unified check may no longer be necessary)
>> + *
>> + * The PPTT table must be rev 3 or later,
>> + *
>> + * If one CPUs L2 is shared with another as L3, this function will return
>> + * an unpredictable value.
>> + *
>> + * Return: -ENOENT if the PPTT doesn't exist, the revision isn't supported or
>> + * the cache cannot be found.
>> + * Otherwise returns a value which represents the level of the specified cache.
>> + */
>> +int find_acpi_cache_level_from_id(u32 cache_id)
>> +{
>> + u32 acpi_cpu_id;
>> + int level, cpu, num_levels;
>> + struct acpi_pptt_cache *cache;
>> + struct acpi_table_header *table;
>> + struct acpi_pptt_cache_v1 *cache_v1;
>> + struct acpi_pptt_processor *cpu_node;
>> +
>> + table = acpi_get_pptt();
>> + if (!table)
>> + return -ENOENT;
>> +
>> + if (table->revision < 3)
>> + return -ENOENT;
>> +
>> + for_each_possible_cpu(cpu) {
>> + acpi_cpu_id = get_acpi_id_for_cpu(cpu);
>> + cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
>> + if (!cpu_node)
>> + return -ENOENT;
>> + num_levels = acpi_count_levels(table, cpu_node, NULL);
>> +
>> + /* Start at 1 for L1 */
>> + for (level = 1; level <= num_levels; level++) {
>> + cache = acpi_find_cache_node(table, acpi_cpu_id,
>> + ACPI_PPTT_CACHE_TYPE_UNIFIED,
>> + level, &cpu_node);
>> + if (!cache)
>> + continue;
>> +
>> + cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
>> + cache,
>> + sizeof(struct acpi_pptt_cache));
>
> sizeof(*cache) to me makes this more obvious.
Would be the only instance of this in the file - but I agree its more readable, and
results in fewer line breaks, which also helps.
>> +
>> + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
>> + cache_v1->cache_id == cache_id)
>> + return level;
>> + }
>> + }
>> +
>> + return -ENOENT;
>> +}
Thanks,
James
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