Hi Jonathan,

On 1/6/26 11:21, Jonathan Cameron wrote:

On Fri, 19 Dec 2025 18:11:25 +0000
Ben Horgan [off-list ref] wrote:

quoted

From: James Morse <james.morse@arm.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@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>

one comment inline.
I messed around with GENMASK + field_prep()/field_get() - new
versions of these with no need for runtime constant masks, but
it ended up as not that much more readable than what you have here.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

quoted

---
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;

Given I think you restrict mpam_pmg_max to be power of 2 elsewhere,
doesn't this end up the same as something like
	return mpam_pmg_max * resctrl_arch_get_num_closid(NULL);
Maybe its worth keeping it in the form you have here as
it sort of provides documentation for how you pack those IDs

We only warn if (mpam_pmg_max + 1) is a power of 2 and so I'll keep this
as it is, although yours is equivalent in the expected case.

quoted

+}

Thanks,

Ben