linux-kernel - [PATCH v2 23/45] arm_mpam: resctrl: Add rmid index helpers

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Message-ID: <20251219181147.3404071-24-ben.horgan@arm.com>
Date: Fri, 19 Dec 2025 18:11:25 +0000
From: Ben Horgan <ben.horgan@....com>
To: ben.horgan@....com
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Subject: [PATCH v2 23/45] arm_mpam: resctrl: Add rmid index helpers

From: James Morse <james.morse@....com>

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@....com>
Signed-off-by: Ben Horgan <ben.horgan@....com>
---
Changes since rfc:
Use ~0U instead of ~0 in lhs of left shift
---
 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 4275b1a85887..bdbc5504964b 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 = ~(~0U << 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
-- 
2.43.0