[RFC PATCH 03/38] arm64: mpam: Advertise the CPUs MPAM limits to the driver

James Morse
2025-12-05T21:59:41Z

Requestors need to populate the MPAM fields for any traffic they send
on the interconnect. For the CPUs these values are taken from the
corresponding MPAMy_ELx register. Each requestor may have a limit on
the largest PARTID or PMG value that can be used. The MPAM driver has
to determine the system-wide minimum supported PARTID and PMG values.

To do this, the driver needs to be told what each requestor's
limit is.

CPUs are special, but this infrastructure is also needed for the
SMMU and GIC ITS. Call the helper to tell the MPAM driver what the
CPUs can do.

The return value can be ignored by the arch code as it runs well
before the MPAM driver starts probing.

Signed-off-by: James Morse <james.morse@arm.com>
---
arch/arm64/kernel/mpam.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c
index 9866d2ca0faa..e6feff2324ac 100644
--- a/arch/arm64/kernel/mpam.c
+++ b/arch/arm64/kernel/mpam.c
@@ -3,6 +3,7 @@

#include <asm/mpam.h>

+#include <linux/arm_mpam.h>
#include <linux/jump_label.h>
#include <linux/percpu.h>

@@ -11,3 +12,14 @@ DEFINE_PER_CPU(u64, arm64_mpam_default);
DEFINE_PER_CPU(u64, arm64_mpam_current);

u64 arm64_mpam_global_default;
+
+static int __init arm64_mpam_register_cpus(void)
+{
+ u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
+ u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr);
+ u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr);
+
+ return mpam_register_requestor(partid_max, pmg_max);
+}
+/* Must occur before mpam_msc_driver_init() from subsys_initcall() */
+arch_initcall(arm64_mpam_register_cpus)
--
2.39.5