[PATCH] arm_mpam: Only program MATCH_PMG when the monitor supports it

[Ping Li]

Hi Ben,

Sorry to bother you again. I was looking at how the driver derives
mpam_pmg_max, and I think there is a similar blind spot:

mpam_msc_hw_probe() folds every MSC's MPAMF_IDR.PMG_MAX into the
global mpam_pmg_max, regardless of whether the MSC has any monitors.

Concretely, on our platform the DSU has no monitors and reports
PMG_MAX=1. Our memory controller MSC has monitors and currently
reports PMG_MAX=0, but if we later add PMG support and report
PMG_MAX=31, the global value would still be clamped to 1 by the DSU,
and resctrl would only expose 2 RMIDs per CLOSID instead of 32.

Should the convergence only consider MSCs that have monitors?
The PE-side value from MPAMIDR_EL1.PMG_MAX would still apply, as
that is the maximum PMG the cores can tag traffic with.

Thanks,
Ping