Re: [RFC PATCH 13/36] arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate

Hi Catalin,

On 24/07/2025 13:09, Catalin Marinas wrote:

On Fri, Jul 11, 2025 at 06:36:25PM +0000, James Morse wrote:

quoted

Probing MPAM is convoluted. MSCs that are integrated with a CPU may
only be accessible from those CPUs, and they may not be online.
Touching the hardware early is pointless as MPAM can't be used until
the system-wide common values for num_partid and num_pmg have been
discovered.

Start with driver probe/remove and mapping the MSC.

quoted

 arch/arm64/Kconfig                          |   1 +
 drivers/platform/arm64/Kconfig              |   1 +
 drivers/platform/arm64/Makefile             |   1 +
 drivers/platform/arm64/mpam/Kconfig         |  10 +
 drivers/platform/arm64/mpam/Makefile        |   4 +
 drivers/platform/arm64/mpam/mpam_devices.c  | 336 ++++++++++++++++++++
 drivers/platform/arm64/mpam/mpam_internal.h |  62 ++++
 7 files changed, 415 insertions(+)
 create mode 100644 drivers/platform/arm64/mpam/Kconfig
 create mode 100644 drivers/platform/arm64/mpam/Makefile
 create mode 100644 drivers/platform/arm64/mpam/mpam_devices.c
 create mode 100644 drivers/platform/arm64/mpam/mpam_internal.h

Bikeshedding: why not drivers/resctrl to match fs/resctrl? We wouldn't
need the previous patch either to move the arm64 platform drivers.

Initially because I don't see any other architecture having an MMIO interface to this
stuff, and didn't want a 'top level' driver directory for a single driver. But, re-reading
RISC-Vs CBQRI[0] it turns out that theirs is memory mapped...

I'm not an expert on resctrl but the MPAM code looks more like a backend
for the resctrl support, so it makes more sense to do as we did for
other drivers like irqchip, iommu.

Only because there are many irqchip or iommu. I'm not a fan of drivers/mpam, but
drivers/resctrl would suit RISC-V too. (I'll check with Drew)


Thanks,

James

[0] https://patchew.org/linux/20230419111111.477118-1-dfustini@baylibre.com/