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

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

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.

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,