[PATCH v3 3/9] arm_mpam: Disable Narrow-PARTID when MBA lacks support

[Zeng Heng]

MPAM supports mixed systems with MSCs that may or may not implement
Narrow-PARTID. However, when the MBA MSC uses percentage-based throttling
(non-bitmap partition control) and lacks Narrow-PARTID support,
resctrl cannot correctly apply control group configurations across
multiple PARTIDs.

Since there is no straightforward way to program compatible control
values in this scenario, disable Narrow-PARTID system-wide when
detected. The detection occurs at initialization time on the first
call to get_num_reqpartid() from mpam_resctrl_pick_counters(),
which is guaranteed to occur after mpam_resctrl_pick_mba() has
set up the MBA resource class.

If MBA MSCs lack Narrow-PARTID support, get_num_reqpartid() falls back
to returning the number of internal PARTIDs (mpam_intpartid_max).

Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
---
 drivers/resctrl/mpam_resctrl.c | 38 +++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index 222ea1d199e1..1b18c095cfce 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -240,9 +240,45 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *ignored)
 	return mpam_intpartid_max + 1;
 }
 
+/*
+ * Determine the effective number of PARTIDs available for resctrl.
+ *
+ * This function performs a one-time check to determine if Narrow-PARTID
+ * can be used. It must be called after mpam_resctrl_pick_mba() has
+ * initialized the MBA resource, as the MBA class properties are used
+ * to detect Narrow-PARTID support.
+ *
+ * The first call occurs in mpam_resctrl_pick_counters(), ensuring the
+ * prerequisite initialization is complete.
+ */
+static u32 get_num_reqpartid(void)
+{
+	struct mpam_resctrl_res *res;
+	struct rdt_resource *r_mba;
+	struct mpam_props *cprops;
+	static bool first = true;
+
+	if (first) {
+		r_mba = resctrl_arch_get_resource(RDT_RESOURCE_MBA);
+		res = container_of(r_mba, struct mpam_resctrl_res, resctrl_res);
+		if (!res->class)
+			goto out;
+
+		/* If MBA MSCs lack Narrow-PARTID support, roll back. */
+		cprops = &res->class->props;
+		if (!mpam_has_feature(mpam_feat_partid_nrw, cprops))
+			mpam_partid_max = mpam_intpartid_max;
+
+	}
+
+out:
+	first = false;
+	return mpam_partid_max + 1;
+}
+
 u32 resctrl_arch_system_num_rmid_idx(void)
 {
-	return (mpam_pmg_max + 1) * (mpam_partid_max + 1);
+	return (mpam_pmg_max + 1) * get_num_reqpartid();
 }
 
 u32 resctrl_arch_rmid_idx_encode(u32 closid, u32 rmid)
-- 
2.25.1