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

[Gavin Shan <gshan@redhat.com>]

Hi Ben,

On 7/16/26 7:26 PM, Ben Horgan wrote:
> 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@arm.com>
>>> ---
>>>    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.
> 

Looks good to me, thanks!

> Thanks,
> 
> Ben
> 

Thanks,
Gavin

>>
>>> 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
>>
>