Re: [PATCH v11 02/13] arm_mpam: propagate MSC access errors for hw_probe functions

[Ben Horgan <ben.horgan@arm.com>]

Hi Andre,

On 30/09/2026 16:57, Andre Przywara wrote:
> Hi Ben,
> 
> On 9/30/26 16:01, Ben Horgan wrote:
>> Hi Andre,
>>
>> On 24/09/2026 16:27, Andre Przywara wrote:
>>> Allow the functions probing for MSC hardware and features to return an
>>> error, and propagate read and write errors from the lower level up.
>>> This uses some "scoped cleanup" functions like scoped_guard() and
>>> ACQUIRE() to avoid the complexity of error handling when a lock has been
>>> taken. Since the mon_sel_lock is a bit special (even more so in an
>>> upcoming patch), we define a new GUARD type for it.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>> Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
>>> Reviewed-by: Ben Horgan <ben.horgan@arm.com>
>>> Reviewed-by: Gavin Shan <gshan@redhat.com>
>>> Tested-by: Gavin Shan <gshan@redhat.com> # on NVIDIA Grace Hopper
>>> ---
>>>   drivers/resctrl/mpam_devices.c  | 126 +++++++++++++++++++++-----------
>>>   drivers/resctrl/mpam_internal.h |   4 +
>>>   2 files changed, 87 insertions(+), 43 deletions(-)
>>>
>>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>>> index c7686d3799653..22069e7f7bb05 100644
>>> --- a/drivers/resctrl/mpam_devices.c
>>> +++ b/drivers/resctrl/mpam_devices.c
>>> @@ -798,38 +798,46 @@ static bool mpam_ris_hw_probe_csu_nrdy(struct mpam_msc_ris *ris)
>>>       bool can_set, can_clear;
>>>       struct mpam_msc *msc = ris->vmsc->msc;
>>>   -    if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
>>> +    ACQUIRE(mon_sel_lock, guard)(msc);
>>> +    if (ACQUIRE_ERR(mon_sel_lock, &guard))
>>>           return false;
>>>         mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, 0) |
>>>             FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
>>> -    mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
>>> +    if (mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel))
>>> +        return false;
>>>         /* Hardware might ignore nrdy if it's not enabled */
>>>       ctl_val = MSMON_CFG_CSU_CTL_TYPE_CSU;
>>>       ctl_val |= MSMON_CFG_x_CTL_MATCH_PARTID;
>>>       ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
>>>       ctl_val |= MSMON_CFG_x_CTL_EN;
>>> -    mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0);
>>> -    mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
>>> +    if (mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0))
>>> +        return false;
>>> +    if (mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val))
>>> +        return false;
>>>   -    _mpam_write_monsel_reg(msc, MSMON_CSU, MSMON___NRDY);
>>> -    _mpam_read_monsel_reg(msc, MSMON_CSU, &now);
>>> +    if (_mpam_write_monsel_reg(msc, MSMON_CSU, MSMON___NRDY))
>>> +        return false;
>>> +    if (_mpam_read_monsel_reg(msc, MSMON_CSU, &now))
>>> +        return false;
>>>       can_set = now & MSMON___NRDY;
>>>   -    _mpam_write_monsel_reg(msc, MSMON_CSU, 0);
>>> +    if (_mpam_write_monsel_reg(msc, MSMON_CSU, 0))
>>> +        return false;
>>>       /* Configuration change to try and coax hardware into setting nrdy */
>>> -    mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0x1);
>>> -    _mpam_read_monsel_reg(msc, MSMON_CSU, &now);
>>> +    if (mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0x1))
>>> +        return false;
>>> +    if (_mpam_read_monsel_reg(msc, MSMON_CSU, &now))
>>> +        return false;
>>>       can_clear = !(now & MSMON___NRDY);
>>> -    mpam_mon_sel_unlock(msc);
>>>         return (!can_set || !can_clear);
>>>   }
>>
>> I've had a look at the Sashiko reports [1] for these patches. I'll call out the things that I feel
>> need answering.
>>
>> As sashiko says, mpam_ris_hw_probe_csu_nrdy(), this swallows the error rather than propagating. It
>> would be better if this returned success/error and the answer to whether or not the h/w supports
>> nrdy separately. As we make other accesses to the msc later it is unlikely this will ever cause a
>> failing probe to report success though.
> 
> Well, what I could offer is to make mpam_ris_hw_probe_csu_nrdy() return an int, with negative values
> meaning an error, 0 meaning false, and 1 being true.
> Then, in the caller, do:
>     err = mpam_ris_hw_probe_csu_nrdy(ris);
>     if (err < 0)
>         return err;
>     hw_managed = err;
> 
> I think a fairly straight-forward change, does this sound OK?

Yep, ok with me.

Thanks,

Ben

> 
> Cheers,
> Andre
>>
>> Thanks,
>>
>> Ben
>>
>> [1] https://sashiko.dev/#/patchset/20260924152739.2865510-1-andre.przywara%40arm.com
>>
>>>   -static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>> +static int mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>   {
>>> -    int err;
>>> +    int fw_has_nrdy_err, err;
>>>       struct mpam_msc *msc = ris->vmsc->msc;
>>>       struct device *dev = &msc->pdev->dev;
>>>       struct mpam_props *props = &ris->props;
>>> @@ -842,7 +850,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>       if (FIELD_GET(MPAMF_IDR_HAS_CCAP_PART, ris->idr)) {
>>>           u32 ccap_features;
>>>   -        mpam_read_partsel_reg(msc, CCAP_IDR, &ccap_features);
>>> +        err = mpam_read_partsel_reg(msc, CCAP_IDR, &ccap_features);
>>> +        if (err)
>>> +            return err;
>>>             props->cmax_wd = FIELD_GET(MPAMF_CCAP_IDR_CMAX_WD, ccap_features);
>>>           if (props->cmax_wd &&
>>> @@ -867,7 +877,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>       if (FIELD_GET(MPAMF_IDR_HAS_CPOR_PART, ris->idr)) {
>>>           u32 cpor_features;
>>>   -        mpam_read_partsel_reg(msc, CPOR_IDR, &cpor_features);
>>> +        err = mpam_read_partsel_reg(msc, CPOR_IDR, &cpor_features);
>>> +        if (err)
>>> +            return err;
>>>             props->cpbm_wd = FIELD_GET(MPAMF_CPOR_IDR_CPBM_WD, cpor_features);
>>>           if (props->cpbm_wd)
>>> @@ -877,8 +889,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>       /* Memory bandwidth partitioning */
>>>       if (FIELD_GET(MPAMF_IDR_HAS_MBW_PART, ris->idr)) {
>>>           u32 mbw_features;
>>> -
>>> -        mpam_read_partsel_reg(msc, MBW_IDR, &mbw_features);
>>> +        err = mpam_read_partsel_reg(msc, MBW_IDR, &mbw_features);
>>> +        if (err)
>>> +            return err;
>>>             /* portion bitmap resolution */
>>>           props->mbw_pbm_bits = FIELD_GET(MPAMF_MBW_IDR_BWPBM_WD, mbw_features);
>>> @@ -907,8 +920,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>       /* Priority partitioning */
>>>       if (FIELD_GET(MPAMF_IDR_HAS_PRI_PART, ris->idr)) {
>>>           u32 pri_features;
>>> -
>>> -        mpam_read_partsel_reg(msc, PRI_IDR, &pri_features);
>>> +        err = mpam_read_partsel_reg(msc, PRI_IDR, &pri_features);
>>> +        if (err)
>>> +            return err;
>>>             props->intpri_wd = FIELD_GET(MPAMF_PRI_IDR_INTPRI_WD, pri_features);
>>>           if (props->intpri_wd && FIELD_GET(MPAMF_PRI_IDR_HAS_INTPRI, pri_features)) {
>>> @@ -929,20 +943,24 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>       if (FIELD_GET(MPAMF_IDR_HAS_MSMON, ris->idr)) {
>>>           u32 msmon_features;
>>>   -        mpam_read_partsel_reg(msc, MSMON_IDR, &msmon_features);
>>> +        err = mpam_read_partsel_reg(msc, MSMON_IDR, &msmon_features);
>>> +        if (err)
>>> +            return err;
>>>             /*
>>>            * If the firmware max-nrdy-us property is missing, the
>>>            * CSU counters can't be used. Should we wait forever?
>>>            */
>>> -        err = device_property_read_u32(&msc->pdev->dev,
>>> -                           "arm,not-ready-us",
>>> -                           &msc->nrdy_usec);
>>> +        fw_has_nrdy_err = device_property_read_u32(&msc->pdev->dev,
>>> +                               "arm,not-ready-us",
>>> +                               &msc->nrdy_usec);
>>>             if (FIELD_GET(MPAMF_MSMON_IDR_MSMON_CSU, msmon_features)) {
>>>               u32 csumonidr;
>>>   -            mpam_read_partsel_reg(msc, CSUMON_IDR, &csumonidr);
>>> +            err = mpam_read_partsel_reg(msc, CSUMON_IDR, &csumonidr);
>>> +            if (err)
>>> +                return err;
>>>                 props->num_csu_mon = FIELD_GET(MPAMF_CSUMON_IDR_NUM_MON, csumonidr);
>>>               if (props->num_csu_mon) {
>>> @@ -960,7 +978,7 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>                    * Accept the missing firmware property if NRDY appears
>>>                    * un-implemented.
>>>                    */
>>> -                if (err && hw_managed)
>>> +                if (fw_has_nrdy_err && hw_managed)
>>>                       dev_err_once(dev, "Counters are not usable because not-ready timeout was
>>> not provided by firmware.");
>>>               }
>>>           }
>>> @@ -968,7 +986,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>               bool has_long;
>>>               u32 mbwumon_idr;
>>>   -            mpam_read_partsel_reg(msc, MBWUMON_IDR, &mbwumon_idr);
>>> +            err = mpam_read_partsel_reg(msc, MBWUMON_IDR, &mbwumon_idr);
>>> +            if (err)
>>> +                return err;
>>>                 props->num_mbwu_mon = FIELD_GET(MPAMF_MBWUMON_IDR_NUM_MON, mbwumon_idr);
>>>               if (props->num_mbwu_mon) {
>>> @@ -1001,16 +1021,22 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>>>           u16 partid_max;
>>>           u32 nrwidr;
>>>   -        mpam_read_partsel_reg(msc, PARTID_NRW_IDR, &nrwidr);
>>> +        err = mpam_read_partsel_reg(msc, PARTID_NRW_IDR, &nrwidr);
>>> +        if (err)
>>> +            return err;
>>> +
>>>           partid_max = FIELD_GET(MPAMF_PARTID_NRW_IDR_INTPARTID_MAX, nrwidr);
>>>             mpam_set_feature(mpam_feat_partid_nrw, props);
>>>           msc->partid_max = min(msc->partid_max, partid_max);
>>>       }
>>> +
>>> +    return 0;
>>>   }
>>>     static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>>   {
>>> +    int ret;
>>>       u64 idr;
>>>       u16 partid_max;
>>>       u8 ris_idx, pmg_max;
>>> @@ -1025,11 +1051,15 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>>       }
>>>         /* Grab an IDR value to find out how many RIS there are */
>>> -    mutex_lock(&msc->part_sel_lock);
>>> -    mpam_msc_read_idr(msc, &idr);
>>> -    mpam_read_partsel_reg(msc, IIDR, &msc->iidr);
>>> +    scoped_guard(mutex, &msc->part_sel_lock) {
>>> +        ret = mpam_msc_read_idr(msc, &idr);
>>> +        if (ret)
>>> +            return ret;
>>>   -    mutex_unlock(&msc->part_sel_lock);
>>> +        ret = mpam_read_partsel_reg(msc, IIDR, &msc->iidr);
>>> +        if (ret)
>>> +            return ret;
>>> +    }
>>>         mpam_enable_quirks(msc);
>>>   @@ -1040,10 +1070,15 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>>       msc->pmg_max = FIELD_GET(MPAMF_IDR_PMG_MAX, idr);
>>>         for (ris_idx = 0; ris_idx <= msc->ris_max; ris_idx++) {
>>> -        mutex_lock(&msc->part_sel_lock);
>>> -        __mpam_part_sel(ris_idx, 0, msc);
>>> -        mpam_msc_read_idr(msc, &idr);
>>> -        mutex_unlock(&msc->part_sel_lock);
>>> +        scoped_guard(mutex, &msc->part_sel_lock) {
>>> +            ret = __mpam_part_sel(ris_idx, 0, msc);
>>> +            if (ret)
>>> +                return ret;
>>> +
>>> +            ret = mpam_msc_read_idr(msc, &idr);
>>> +            if (ret)
>>> +                return ret;
>>> +        }
>>>             partid_max = FIELD_GET(MPAMF_IDR_PARTID_MAX, idr);
>>>           pmg_max = FIELD_GET(MPAMF_IDR_PMG_MAX, idr);
>>> @@ -1051,17 +1086,22 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>>           msc->pmg_max = min(msc->pmg_max, pmg_max);
>>>           msc->has_extd_esr = FIELD_GET(MPAMF_IDR_HAS_EXTD_ESR, idr);
>>>   -        mutex_lock(&mpam_list_lock);
>>> -        ris = mpam_get_or_create_ris(msc, ris_idx);
>>> -        mutex_unlock(&mpam_list_lock);
>>> -        if (IS_ERR(ris))
>>> -            return PTR_ERR(ris);
>>> +        scoped_guard(mutex, &mpam_list_lock) {
>>> +            ris = mpam_get_or_create_ris(msc, ris_idx);
>>> +            if (IS_ERR(ris))
>>> +                return PTR_ERR(ris);
>>> +        }
>>>           ris->idr = idr;
>>>   -        mutex_lock(&msc->part_sel_lock);
>>> -        __mpam_part_sel(ris_idx, 0, msc);
>>> -        mpam_ris_hw_probe(ris);
>>> -        mutex_unlock(&msc->part_sel_lock);
>>> +        scoped_guard(mutex, &msc->part_sel_lock) {
>>> +            ret = __mpam_part_sel(ris_idx, 0, msc);
>>> +            if (ret)
>>> +                return ret;
>>> +
>>> +            ret = mpam_ris_hw_probe(ris);
>>> +            if (ret)
>>> +                return ret;
>>> +        }
>>>       }
>>>         /* Clear any stale errors */
>>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
>>> index def0e3a65c230..68a6cf2b9cc73 100644
>>> --- a/drivers/resctrl/mpam_internal.h
>>> +++ b/drivers/resctrl/mpam_internal.h
>>> @@ -162,6 +162,10 @@ static inline void mpam_mon_sel_lock_init(struct mpam_msc *msc)
>>>       raw_spin_lock_init(&msc->_mon_sel_lock);
>>>   }
>>>   +DEFINE_GUARD(mon_sel, struct mpam_msc *,
>>> +         mpam_mon_sel_lock(_T), mpam_mon_sel_unlock(_T));
>>> +DEFINE_GUARD_COND(mon_sel, _lock, mpam_mon_sel_lock(_T), _RET);
>>> +
>>>   /* Bits for mpam features bitmaps */
>>>   enum mpam_device_features {
>>>       mpam_feat_cpor_part,
>>
>