Hi James,

On 8/28/25 16:58, James Morse wrote:

Hi Ben,

On 27/08/2025 09:53, Ben Horgan wrote:

quoted

On 8/22/25 16:29, James Morse wrote:

quoted

The bulk of the MPAM driver lives outside the arch code because it
largely manages MMIO devices that generate interrupts. The driver
needs a Kconfig symbol to enable it, as MPAM is only found on arm64
platforms, that is where the Kconfig option makes the most sense.

This Kconfig option will later be used by the arch code to enable
or disable the MPAM context-switch code, and registering the CPUs
properties with the MPAM driver.

quoted

quoted

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index e9bbfacc35a6..658e47fc0c5a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -2060,6 +2060,23 @@ config ARM64_TLB_RANGE
 	  ARMv8.4-TLBI provides TLBI invalidation instruction that apply to a
 	  range of input addresses.
 
+config ARM64_MPAM
+	bool "Enable support for MPAM"
+	help
+	  Memory Partitioning and Monitoring is an optional extension
+	  that allows the CPUs to mark load and store transactions with
+	  labels for partition-id and performance-monitoring-group.
+	  System components, such as the caches, can use the partition-id
+	  to apply a performance policy. MPAM monitors can use the
+	  partition-id and performance-monitoring-group to measure the
+	  cache occupancy or data throughput.
+
+	  Use of this extension requires CPU support, support in the
+	  memory system components (MSC), and a description from firmware
+	  of where the MSC are in the address space.
+
+	  MPAM is exposed to user-space via the resctrl pseudo filesystem.
+
 endmenu # "ARMv8.4 architectural features"

quoted

Should this be moved to "ARMv8.2 architectural features" rather than the
8.4 menu? In the arm reference manual, version L.b, I see FEAT_MPAM
listed in the section A2.2.3.1 Features added to the Armv8.2 extension
in later releases.

Hmmm, I don't think we've done that anywhere else. I'm only aware of one v8.2 platform
that had it, and those are not widely available. As it was a headline v8.4 feature I'd
prefer to keep it there.

I think its more confusing to put it under v8.2!

Ok, always best to minimise confusion. Keep it in v8.4.
 >

Thanks,

James

-- 
Thanks,

Ben