[PATCH v6 4/7] fs/resctrl: Add monitor property 'mbm_cntr_assign_fixed'

[Ben Horgan <ben.horgan@arm.com>]

Commit

  3b497c3f4f04 ("fs/resctrl: Introduce the interface to display monitoring modes")

introduced CONFIG_RESCTRL_ASSIGN_FIXED but left adding the Kconfig
entry until it was necessary. The counter assignment mode is fixed in
MPAM, even when there are assignable counters, and so addressing this
is needed to support MPAM.

To avoid the burden of another Kconfig entry, replace
CONFIG_RESCTRL_ASSIGN_FIXED with a new property in 'struct resctrl_mon',
'mbm_cntr_assign_fixed' to be set by the architecture.

Do not request the architecture to change the counter assignment mode if it
does not support doing so. Provide insight to user space about why such a
request fails.

Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since v2:
Change to a resctrl_mon property rather than a arch hook
Update the commit message to mention the property

Changes since v4:
fix -> fixed in comment
commit message drop x86
In commit message add "to be set by the architecture" and update
last paragraph.

Changes since v5:
Add Reinette's R-b
---
 fs/resctrl/monitor.c    | 8 +++++++-
 include/linux/resctrl.h | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 916f7a9d5658..5fbcc64e50ce 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1456,7 +1456,7 @@ int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
 		else
 			seq_puts(s, "[default]\n");
 
-		if (!IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
+		if (!r->mon.mbm_cntr_assign_fixed) {
 			if (enabled)
 				seq_puts(s, "default\n");
 			else
@@ -1507,6 +1507,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 	}
 
 	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		if (r->mon.mbm_cntr_assign_fixed) {
+			ret = -EINVAL;
+			rdt_last_cmd_puts("Counter assignment mode is not configurable\n");
+			goto out_unlock;
+		}
+
 		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
 		if (ret)
 			goto out_unlock;
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 06e8c72e8660..73ff522448a0 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -294,6 +294,7 @@ enum resctrl_schema_fmt {
  * @mbm_assign_on_mkdir:	True if counters should automatically be assigned to MBM
  *				events of monitor groups created via mkdir.
  * @mbm_cntr_configurable:	True if assignable counters are configurable.
+ * @mbm_cntr_assign_fixed:	True if the counter assignment mode is fixed.
  */
 struct resctrl_mon {
 	u32			num_rmid;
@@ -302,6 +303,7 @@ struct resctrl_mon {
 	bool			mbm_cntr_assignable;
 	bool			mbm_assign_on_mkdir;
 	bool			mbm_cntr_configurable;
+	bool			mbm_cntr_assign_fixed;
 };
 
 /**
-- 
2.43.0