drivers: base: support cpu cache information interface to userspace via sysfs

This patch adds initial support for providing processor cache information
to userspace through sysfs interface. This is based on already existing
implementations(x86, ia64, s390 and powerpc) and hence the interface is
intended to be fully compatible.

The main purpose of this generic support is to avoid further code
duplication to support new architectures and also to unify all the existing
different implementations.

This implementation maintains the hierarchy of cache objects which reflects
the system's cache topology. Cache devices are instantiated as needed as
CPUs come online. The cache information is replicated per-cpu even if they are
shared. A per-cpu array of cache information maintained is used mainly for
sysfs-related book keeping.

It also implements the shared_cpu_map attribute, which is essential for
enabling both kernel and user-space to discover the system's overall cache
topology.

This patch also add the missing ABI documentation for the cacheinfo sysfs
interface already, which is well defined and widely used.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Tested-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-api@vger.kernel.org
Cc: linux390@de.ibm.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-ia64@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: x86@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index acb9bfc89b48..99983e67c13c 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -224,3 +224,50 @@ Description:	Parameters for the Intel P-state driver
                 frequency range.
 
                 More details can be found in Documentation/cpu-freq/intel-pstate.txt
+
+What:           /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
+Date:           July 2014(documented, existed before August 2008)
+Contact:        Sudeep Holla <sudeep.holla@arm.com>
+                Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:    Parameters for the CPU cache attributes
+
+                allocation_policy:
+                        - WriteAllocate: allocate a memory location to a cache line
+                                         on a cache miss because of a write
+                        - ReadAllocate: allocate a memory location to a cache line
+                                        on a cache miss because of a read
+                        - ReadWriteAllocate: both writeallocate and readallocate
+
+                attributes: LEGACY used only on IA64 and is same as write_policy
+
+                coherency_line_size: the minimum amount of data in bytes that gets
+                                     transferred from memory to cache
+
+                level: the cache hierarcy in the multi-level cache configuration
+
+                number_of_sets: total number of sets in the cache, a set is a
+                                collection of cache lines with the same cache index
+
+                physical_line_partition: number of physical cache line per cache tag
+
+                shared_cpu_list: the list of logical cpus sharing the cache
+
+                shared_cpu_map: logical cpu mask containing the list of cpus sharing
+                                the cache
+
+                size: the total cache size in kB
+
+                type:
+                        - Instruction: cache that only holds instructions
+                        - Data: cache that only caches data
+                        - Unified: cache that holds both data and instructions
+
+                ways_of_associativity: degree of freedom in placing a particular block
+                                        of memory in the cache
+
+                write_policy:
+                        - WriteThrough: data is written to both the cache line
+                                        and to the block in the lower-level memory
+                        - WriteBack: data is written only to the cache line and
+                                     the modified cache line is written to main
+                                     memory only when it is replaced