[RFC PATCH 14/38] arm_mpam: resctrl: Add rmid index helpers

James Morse
2025-12-05T22:00:25Z

Because MPAM's pmg aren't identical to RDT's rmid, resctrl handles
some data structures by index. This allows x86 to map indexes to
RMID, and MPAM to map them to partid-and-pmg.

Add the helpers to do this.

Signed-off-by: James Morse <james.morse@arm.com>
---
drivers/resctrl/mpam_resctrl.c | 28 ++++++++++++++++++++++++++++
include/linux/arm_mpam.h | 3 +++
2 files changed, 31 insertions(+)

diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index d5f75ed67e46..19d70d00bbcc 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -120,6 +120,34 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *ignored)
return mpam_partid_max + 1;
}

+u32 resctrl_arch_system_num_rmid_idx(void)
+{
+ u8 closid_shift = fls(mpam_pmg_max);
+ u32 num_partid = resctrl_arch_get_num_closid(NULL);
+
+ return num_partid << closid_shift;
+}
+
+u32 resctrl_arch_rmid_idx_encode(u32 closid, u32 rmid)
+{
+ u8 closid_shift = fls(mpam_pmg_max);
+
+ WARN_ON_ONCE(closid_shift > 8);
+
+ return (closid << closid_shift) | rmid;
+}
+
+void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
+{
+ u8 closid_shift = fls(mpam_pmg_max);
+ u32 pmg_mask = ~(~0 << closid_shift);
+
+ WARN_ON_ONCE(closid_shift > 8);
+
+ *closid = idx >> closid_shift;
+ *rmid = idx & pmg_mask;
+}
+
void resctrl_arch_sched_in(struct task_struct *tsk)
{
lockdep_assert_preemption_disabled();
diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index ba0312b55d9f..385554ceb452 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h
@@ -59,6 +59,9 @@ void resctrl_arch_set_cpu_default_closid_rmid(int cpu, u32 closid, u32 rmid);
void resctrl_arch_sched_in(struct task_struct *tsk);
bool resctrl_arch_match_closid(struct task_struct *tsk, u32 closid);
bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 closid, u32 rmid);
+u32 resctrl_arch_rmid_idx_encode(u32 closid, u32 rmid);
+void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid);
+u32 resctrl_arch_system_num_rmid_idx(void);

/**
* mpam_register_requestor() - Register a requestor with the MPAM driver
--
2.39.5