arm_mpam: Apply T241-MPAM-6 to 63-bit counters
authorShanker Donthineni <sdonthineni@nvidia.com>
Fri, 31 Jul 2026 17:52:43 +0000 (18:52 +0100)
committerWill Deacon <will@kernel.org>
Sun, 2 Aug 2026 09:33:43 +0000 (09:33 +0000)
commit2c43aced9be353f8428678a75495ca9d631dc927
tree92b3abd04ec1bc699a0ca0b6e64ec4477de605af
parent6b4ee75215c9dbcf6a0fd8cf7af2449906e2932c
arm_mpam: Apply T241-MPAM-6 to 63-bit counters

T241-MPAM-6 causes all MBWU counter formats to count 64-byte
requests instead of bytes. Commit dc48eb1ff27c excluded the 63-bit
MSMON_MBWU_LWD format while scaling the shorter counters. Systems
selecting the preferred 63-bit counter consequently report bandwidth
values that are 64 times too small.

Apply the scale to both the sampled value and overflow correction for
the 63-bit format. Unsigned arithmetic retains modulo-u64 behavior
when the scaled counter range exceeds u64.

Fixes: dc48eb1ff27c ("arm_mpam: Add workaround for T241-MPAM-6")
Link: https://lore.kernel.org/lkml/20240816131432.993859-1-sdonthineni@nvidia.com/
Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
drivers/resctrl/mpam_devices.c