arm_mpam: Add cpuhp callbacks to probe MSC hardware

Because an MSC can only by accessed from the CPUs in its cpu-affinity
set we need to be running on one of those CPUs to probe the MSC
hardware.

Do this work in the cpuhp callback. Probing the hardware will only
happen before MPAM is enabled, walk all the MSCs and probe those we can
reach that haven't already been probed as each CPU's online call is made.

This adds the low-level MSC register read accessors.

Once all MSCs reported by the firmware have been probed from a CPU in
their respective cpu-affinity set, the probe-time cpuhp callbacks are
replaced.  The replacement callbacks will ultimately need to handle
save/restore of the runtime MSC state across power transitions, but for
now there is nothing to do in them: so do nothing.

The architecture's context switch code will be enabled by a static-key,
this can be set by mpam_enable(), but must be done from process context,
not a cpuhp callback because both take the cpuhp lock.
Whenever a new MSC has been probed, the mpam_enable() work is scheduled
to test if all the MSCs have been probed. If probing fails, mpam_disable()
is scheduled to unregister the cpuhp callbacks and free memory.

CC: Lecopzer Chen <lecopzerc@nvidia.com>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com>
Tested-by: Gavin Shan <gshan@redhat.com>
Tested-by: Zeng Heng <zengheng4@huawei.com>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 51f791cc207b..4e1538d29783 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -48,6 +48,7 @@ struct mpam_msc {
 	 * properties become read-only and the lists are protected by SRCU.
 	 */
 	struct mutex		probe_lock;
+	bool			probed;
 	unsigned long		ris_idxs;
 	u32			ris_max;
 
@@ -137,6 +138,10 @@ struct mpam_msc_ris {
 extern struct srcu_struct mpam_srcu;
 extern struct list_head mpam_classes;
 
+/* Scheduled work callback to enable mpam once all MSC have been probed */
+void mpam_enable(struct work_struct *work);
+void mpam_disable(struct work_struct *work);
+
 int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
 				   cpumask_t *affinity);