Re: [PATCH v9 10/12] arm_mpam: add MPAM-Fb MSC firmware access support

On 8/7/2026 4:24 PM, Andre Przywara wrote:
> The Arm MPAM Firmware-backed (Fb) Profile document[1] describes an
> alternative way of accessing the "Memory System Components" (MSC) in an
> MPAM enabled system.
> 
> Normally the MSCs are MMIO mapped, but in some implementations this
> might not be possible (MSC located outside of the local socket, MSC
> mapped secure-only) or desirable (direct MMIO access too slow or needs
> to be mediated through a control processor). MPAM-fb standardises a
> protocol to abstract MSC accesses, building on the SCMI protocol.
> 
> Add functions that do an MSC read or write access by redirecting the
> request through a firmware interface. For now this done via an ACPI
> PCC shared memory and mailbox combination.
> 
> Since the protocol used is only a small subset of the full SCMI spec,
> and the SCMI protocol has no full ACPI support anyway, open-code the
> (simple) SCMI message generation, for just the fields we need.
> 
> [1] https://developer.arm.com/documentation/den0144/latest
> 
> Signed-off-by: Andre Przywara <[email protected]>
> Reviewed-by: Jonathan Cameron <[email protected]>
> Tested-by: Ritwick Sharma <[email protected]> # on Arm AGI CPU
> Reviewed-by: Gavin Shan <[email protected]>
> Tested-by: Srivathsa L Rao <[email protected]>
> ---
>   drivers/resctrl/Makefile        |   2 +-
>   drivers/resctrl/mpam_devices.c  |  65 ++++++++--
>   drivers/resctrl/mpam_fb.c       | 211 ++++++++++++++++++++++++++++++++
>   drivers/resctrl/mpam_internal.h |  18 +++
>   include/linux/arm_mpam.h        |   2 +-
>   5 files changed, 284 insertions(+), 14 deletions(-)
>   create mode 100644 drivers/resctrl/mpam_fb.c
> 
> diff --git a/drivers/resctrl/Makefile b/drivers/resctrl/Makefile
> index 4f6d0e81f9b8..097c036724e9 100644
> --- a/drivers/resctrl/Makefile
> +++ b/drivers/resctrl/Makefile
> @@ -1,5 +1,5 @@
Reviewed-by: Srivathsa L Rao <[email protected]>