topology/sysfs: export cluster attributes only if an architectures has support

The cluster_id and cluster_cpus topology sysfs attributes have been
added with commit c5e22fef ("topology: Represent clusters of CPUs
within a die").

They are currently only used for x86, arm64, and riscv (via generic
arch topology), however they are still present with bogus default
values for all other architectures. Instead of enforcing such new
sysfs attributes to all architectures, make them only optional visible
if an architecture opts in by defining both the topology_cluster_id
and topology_cluster_cpumask attributes.

This is similar to what was done when the book and drawer topology
levels were introduced: avoid useless and therefore confusing sysfs
attributes for architectures which cannot make use of them.

This should not break any existing applications, since this is a
new interface introduced with the v5.16 merge window.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20211129130309.3256168-3-hca@linux.ibm.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/admin-guide/cputopology.rst

@@ -11,8 +11,8 @@ Architecture-neutral, drivers/base/topology.c, exports these attributes.
 However, the book and drawer related sysfs files will only be created if
 CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are selected, respectively.
 
-The die hierarchy related sysfs files will only be created if an architecture
-provides the related macros as described below.
+The die and cluster hierarchy related sysfs files will only be created if an
+architecture provides the related macros as described below.
 
 CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are currently only used on s390,
 where they reflect the cpu and cache hierarchy.

drivers/base/topology.c

@@ -50,8 +50,10 @@ define_id_show_func(die_id);
 static DEVICE_ATTR_RO(die_id);
 #endif
 
+#ifdef TOPOLOGY_CLUSTER_SYSFS
 define_id_show_func(cluster_id);
 static DEVICE_ATTR_RO(cluster_id);
+#endif
 
 define_id_show_func(core_id);
 static DEVICE_ATTR_RO(core_id);
@@ -68,9 +70,11 @@ define_siblings_read_func(core_siblings, core_cpumask);
 static BIN_ATTR_RO(core_siblings, 0);
 static BIN_ATTR_RO(core_siblings_list, 0);
 
+#ifdef TOPOLOGY_CLUSTER_SYSFS
 define_siblings_read_func(cluster_cpus, cluster_cpumask);
 static BIN_ATTR_RO(cluster_cpus, 0);
 static BIN_ATTR_RO(cluster_cpus_list, 0);
+#endif
 
 #ifdef TOPOLOGY_DIE_SYSFS
 define_siblings_read_func(die_cpus, die_cpumask);
@@ -105,8 +109,10 @@ static struct bin_attribute *bin_attrs[] = {
 	&bin_attr_thread_siblings_list,
 	&bin_attr_core_siblings,
 	&bin_attr_core_siblings_list,
+#ifdef TOPOLOGY_CLUSTER_SYSFS
 	&bin_attr_cluster_cpus,
 	&bin_attr_cluster_cpus_list,
+#endif
 #ifdef TOPOLOGY_DIE_SYSFS
 	&bin_attr_die_cpus,
 	&bin_attr_die_cpus_list,
@@ -129,7 +135,9 @@ static struct attribute *default_attrs[] = {
 #ifdef TOPOLOGY_DIE_SYSFS
 	&dev_attr_die_id.attr,
 #endif
+#ifdef TOPOLOGY_CLUSTER_SYSFS
 	&dev_attr_cluster_id.attr,
+#endif
 	&dev_attr_core_id.attr,
 #ifdef CONFIG_SCHED_BOOK
 	&dev_attr_book_id.attr,

include/linux/topology.h

@@ -183,6 +183,9 @@ static inline int cpu_to_mem(int cpu)
 #if defined(topology_die_id) && defined(topology_die_cpumask)
 #define TOPOLOGY_DIE_SYSFS
 #endif
+#if defined(topology_cluster_id) && defined(topology_cluster_cpumask)
+#define TOPOLOGY_CLUSTER_SYSFS
+#endif
 
 #ifndef topology_physical_package_id
 #define topology_physical_package_id(cpu)	((void)(cpu), -1)