Re: [PATCH v3 07/16] arm_mpam: __ris_msmon_read(): get rid of nrdy special handling

[Andre Przywara]

Hi Ben,

thanks for having a look!

On 7/15/26 15:39, Ben Horgan wrote:
> Hi Andre,
>
> On 7/10/26 15:45, Andre Przywara wrote:
> > Although so far MSC accesses couldn't fail, there is one special
> > condition that would create an error: when the MBWU counter wouldn't be
> > able to read a stable value, we were setting bit 63 to mark this value
> > as unstable, and return this as an error later.
> > Now since the functions can return a proper error value, we can get rid of
> > this kludge and use the return value directly.
> >
> > Remove the "nrdy" error flag variable, and assign -EBUSY to "ret" to handle
> > this case.
>
> I don't think we want this patch. The h/w can still return (as much as it ever could) and so we
> still need to handle it even if we are no longer augmenting its meaning in software to also indicate
> an unstable 64 bit value.

Mmh, not sure I understand your concern: to me it looks like nrdy is 
some kind of error flag, that we used in absence of a proper error 
return value. Now we have "int ret;", so can use that directly? But to 
me it looks like nothing really changes, or did I miss something?

I have no really strong opinion of this patch, it was more an pportunity 
to consolidate the crude error handling in this function. I am happy to 
drop it, if you like, maybe we can revisit this later.

Cheers,
Andre

> Thanks,
>
> Ben
>
> > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> > ---
> >   drivers/resctrl/mpam_devices.c | 38 +++++++++++++++-------------------
> >   1 file changed, 17 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> > index 84a8715464be..530ac0fe97b5 100644
> > --- a/drivers/resctrl/mpam_devices.c
> > +++ b/drivers/resctrl/mpam_devices.c
> > @@ -1306,7 +1306,6 @@ static void __ris_msmon_read(void *arg)
> >   	u64 now;
> >   	int ret;
> >   	u32 now32;
> > -	bool nrdy = false;
> >   	bool config_mismatch;
> >   	bool overflow = false;
> >   	struct mon_read *m = arg;
> > @@ -1371,14 +1370,18 @@ static void __ris_msmon_read(void *arg)
> >   	switch (m->type) {
> >   	case mpam_feat_msmon_csu:
> >   		ret = mpam_read_monsel_reg(msc, CSU, &now32);
> > +		if (!ret) {
> > +			if ((now32 & MSMON___NRDY))
> > +				ret = -EBUSY;
> > +
> > +			if (mpam_has_quirk(IGNORE_CSU_NRDY, msc) &&
> > +			    m->waited_timeout)
> > +				ret = 0;
> > +		}
> >   		if (ret)
> >   			goto out_unlock;
> > -		nrdy = now32 & MSMON___NRDY;
> > -		now = FIELD_GET(MSMON___VALUE, now32);
> > -
> > -		if (mpam_has_quirk(IGNORE_CSU_NRDY, msc) && m->waited_timeout)
> > -			nrdy = false;
> >   
> > +		now = FIELD_GET(MSMON___VALUE, now32);
> >   		break;
> >   	case mpam_feat_msmon_mbwu_31counter:
> >   	case mpam_feat_msmon_mbwu_44counter:
> > @@ -1394,9 +1397,11 @@ static void __ris_msmon_read(void *arg)
> >   				now = FIELD_GET(MSMON___L_VALUE, now);
> >   		} else {
> >   			ret = mpam_read_monsel_reg(msc, MBWU, &now32);
> > +			if (!ret && (now32 & MSMON___NRDY))
> > +				ret = -EBUSY;
> >   			if (ret)
> >   				goto out_unlock;
> > -			nrdy = now32 & MSMON___NRDY;
> > +
> >   			now = FIELD_GET(MSMON___VALUE, now32);
> >   		}
> >   
> > @@ -1404,9 +1409,6 @@ static void __ris_msmon_read(void *arg)
> >   		    m->type != mpam_feat_msmon_mbwu_63counter)
> >   			now *= 64;
> >   
> > -		if (nrdy)
> > -			break;
> > -
> >   		mbwu_state = &ris->mbwu_state[ctx->mon];
> >   
> >   		if (overflow)
> > @@ -1419,22 +1421,16 @@ static void __ris_msmon_read(void *arg)
> >   		now += mbwu_state->correction;
> >   		break;
> >   	default:
> > -		m->err = -EINVAL;
> > +		ret = -EINVAL;
> >   	}
> > -	mpam_mon_sel_unlock(msc);
> > -
> > -	if (nrdy)
> > -		m->err = -EBUSY;
> > -
> > -	if (!m->err)
> > -		*m->val += now;
> > -
> > -	return;
> >   
> >   out_unlock:
> >   	mpam_mon_sel_unlock(msc);
> >   
> > -	m->err = ret;
> > +	if (ret)
> > +		m->err = ret;
> > +	else
> > +		*m->val += now;
> >   }
> >   
> >   static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)