Re: [PATCH v11 02/13] arm_mpam: propagate MSC access errors for hw_probe functions
From: Ben Horgan
Date: Wed Sep 30 2026 - 14:46:10 EST
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@xxxxxxx>
>>> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxxxxxxxx>
>>> Reviewed-by: Ben Horgan <ben.horgan@xxxxxxx>
>>> Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
>>> Tested-by: Gavin Shan <gshan@xxxxxxxxxx> # 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,
>>
>