Re: [PATCH v1 03/11] arm_mpam: Set mpam_feat_msmon_mbwu_31counter when there are bandwidth counters

[Ben Horgan]

Hi Gavin,

On 7/16/26 05:18, Gavin Shan wrote:
> On 7/10/26 9:55 PM, Ben Horgan wrote:
>> If there are memory bandwidth counters then there are 31 bit counters even
>> if there are also 44 bit counters or 63 bit counters.
>>
>> Set the 31 bit bandwidth counter feature bit whenever there are bandwidth
>> counters.
>>
>> Fixes: fdc29a141d63 ("arm_mpam: Probe for long/lwd mbwu counters")
>> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
>> ---
>>   drivers/resctrl/mpam_devices.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
> 
> It might be worthwhile to put some context in the commit log helping readers
> to correlate to the specification. What I found is something like below in
> section 8.2.1.2 Long MBWU counter and capture of ARM IHI 0099A.a:
> 
> In MSMON_MBWU, the VALUE field is always 31 bits. If MSMON_MBWU_L is implemented,
> the length of the VALUE field is either 63 or 44 bits as set by MPAMF_MBWUMON_IDR.LWD.

How about?

When MPAMF_MSMON_IDR.MSMON_MBWU is 1, MSMON_MBWU is present and has a VALUE field of 31 bits. If
additionally, MPAMF_MBWUMON_IDR.HAS_LONG is 1, then MSMON_MBWU_L is also present and has a VALUE
field of 44 or 63 bits as indicated by MPAMF_MBWUMON_IDR.LWD.

Thanks,

Ben

> 
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index acfa9a4dc2fc..11b10c3bc334 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -930,9 +930,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>                           mpam_set_feature(mpam_feat_msmon_mbwu_63counter, props);
>>                       else
>>                           mpam_set_feature(mpam_feat_msmon_mbwu_44counter, props);
>> -                } else {
>> -                    mpam_set_feature(mpam_feat_msmon_mbwu_31counter, props);
>>                   }
>> +
>> +                mpam_set_feature(mpam_feat_msmon_mbwu_31counter, props);
>>               }
>>           }
>>       }
> 
> Thanks,
> Gavin
>