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Commit dc48eb1ff27c excluded the 63-bit > As described in that commit message, T241-MPAM-6 does not affect LWD counters. Is there another > canonical description of T241-MPAM-6. Otherwise, this just looks like you've discovered a new h/w > bug :) The original commit message for dc48eb1ff27c explicitly states that T241-MPAM-6 affects both MSMON_MBWU and MSMON_MBWU_L:  "The registers MSMON_MBWU_L and MSMON_MBWU return the number of requests rather than the number   of bytes transferred." LWD (when HAS_LONG=1) selects the width/format of MSMON_MBWU_L; it does not identify a separate register outside the scope described above. >> 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. > So, the MSC with IIDR MPAM_IIDR_NVIDIA_T241 has different sizes of long bandwidth counters between > RIS. This seems a bit unusual. Please could you share which RIS have 44 bit long counters and which > have 63 bits. (MPAMF_MBWUMON_IDR.LWD gives this) T241 does not implement RIS (MPAMF_IDR.HAS_RIS=0). Its L3 MSC implements a 63-bit long bandwidth counter, as indicated by HAS_LONG=1 and LWD=1; therefore, there are no per-RIS differences in counter width. The mpam_feat_msmon_mbwu_63counter exclusion in dc48eb1ff27c means the workaround is not applied to the long-counter format implemented by the T241 L3 MSC. This patch removes that exclusion and makes the implementation consistent with the original erratum description and commit message. > Thanks, > > Ben > >> 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 >> --- >> drivers/resctrl/mpam_devices.c | 6 ++---- >> 1 file changed, 2 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c >> index 2f09f4b78bd3b..b68f5599e8dbe 100644 >> --- a/drivers/resctrl/mpam_devices.c >> +++ b/drivers/resctrl/mpam_devices.c >> @@ -1196,8 +1196,7 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type, >> { >> u64 overflow_val = __mpam_msmon_overflow_val(type); >> >> - if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc) && >> - type != mpam_feat_msmon_mbwu_63counter) >> + if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc)) >> overflow_val *= 64; >> >> return overflow_val; >> @@ -1293,8 +1292,7 @@ static void __ris_msmon_read(void *arg) >> now = FIELD_GET(MSMON___VALUE, now); >> } >> >> - if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc) && >> - m->type != mpam_feat_msmon_mbwu_63counter) >> + if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc)) >> now *= 64; >> >> if (nrdy)