Re: [RFC PATCH 20/36] arm_mpam: Probe the hardware features resctrl supports

[James Morse]

Hi Ben,

On 28/07/2025 09:56, Ben Horgan wrote:
> On 7/11/25 19:36, James Morse wrote:
> > Expand the probing support with the control and monitor types
> > we can use with resctrl.

> > diff --git a/drivers/platform/arm64/mpam/mpam_internal.h b/drivers/platform/arm64/mpam/
> > mpam_internal.h
> > index 42a454d5f914..ae6fd1f62cc4 100644
> > --- a/drivers/platform/arm64/mpam/mpam_internal.h
> > +++ b/drivers/platform/arm64/mpam/mpam_internal.h
> > @@ -136,6 +136,55 @@ static inline void mpam_mon_sel_lock_held(struct mpam_msc *msc)
> >           lockdep_assert_preemption_enabled();
> >   }
> >   +/*
> > + * When we compact the supported features, we don't care what they are.
> > + * Storing them as a bitmap makes life easy.
> > + */
> > +typedef u16 mpam_features_t;
> > +
> > +/* Bits for mpam_features_t */
> > +enum mpam_device_features {
> > +    mpam_feat_ccap_part = 0,
> > +    mpam_feat_cpor_part,
> > +    mpam_feat_mbw_part,
> > +    mpam_feat_mbw_min,
> > +    mpam_feat_mbw_max,
> > +    mpam_feat_mbw_prop,
> > +    mpam_feat_msmon,
> > +    mpam_feat_msmon_csu,
> > +    mpam_feat_msmon_csu_capture,
> > +    mpam_feat_msmon_csu_hw_nrdy,
> > +    mpam_feat_msmon_mbwu,
> > +    mpam_feat_msmon_mbwu_capture,
> > +    mpam_feat_msmon_mbwu_rwbw,
> > +    mpam_feat_msmon_mbwu_hw_nrdy,
> > +    mpam_feat_msmon_capt,
> > +    MPAM_FEATURE_LAST,
> > +};
> > +#define MPAM_ALL_FEATURES      ((1 << MPAM_FEATURE_LAST) - 1)
>
> Consider a static assert to check the type is big enough.
>
> static_assert(BITS_PER_TYPE(mpam_features_t) >= MPAM_FEATURE_LAST);

Fancy.
There used to be an uglier one - not sure what happened to it!



Thanks,

James