On Wed, 10 Sep 2025 20:42:51 +0000 James Morse <james.morse@xxxxxxx> wrote: > CPUs can generate traffic with a range of PARTID and PMG values, > but each MSC may also have its own maximum size for these fields. > Before MPAM can be used, the driver needs to probe each RIS on > each MSC, to find the system-wide smallest value that can be used. > The limits from requestors (e.g. CPUs) also need taking into account. > > While doing this, RIS entries that firmware didn't describe are created > under MPAM_CLASS_UNKNOWN. > > While we're here, implement the mpam_register_requestor() call > for the arch code to register the CPU limits. Future callers of this > will tell us about the SMMU and ITS. > > Signed-off-by: James Morse <james.morse@xxxxxxx> Trivial stuff inline. Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx> > --- > Changes since v1: > * Change to lock ordering now that the list-lock mutex isn't held from > the cpuhp call. > * Removed irq-unmaksed assert in requestor register. > * Changed captialisation in print message. > --- > drivers/resctrl/mpam_devices.c | 150 +++++++++++++++++++++++++++++++- > drivers/resctrl/mpam_internal.h | 6 ++ > include/linux/arm_mpam.h | 14 +++ > 3 files changed, 169 insertions(+), 1 deletion(-) > > diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c > index c265376d936b..24dc81c15ec8 100644 > --- a/drivers/resctrl/mpam_devices.c > +++ b/drivers/resctrl/mpam_devices.c > +int mpam_register_requestor(u16 partid_max, u8 pmg_max) > +{ > + int err = 0; > + > + spin_lock(&partid_max_lock); guard() perhaps so you can return early in the error pat and avoid need for local variable err. > + if (!partid_max_init) { > + mpam_partid_max = partid_max; > + mpam_pmg_max = pmg_max; > + partid_max_init = true; > + } else if (!partid_max_published) { > + mpam_partid_max = min(mpam_partid_max, partid_max); > + mpam_pmg_max = min(mpam_pmg_max, pmg_max); > + } else { > + /* New requestors can't lower the values */ > + if (partid_max < mpam_partid_max || pmg_max < mpam_pmg_max) > + err = -EBUSY; > + } > + spin_unlock(&partid_max_lock); > + > + return err; > +} > +EXPORT_SYMBOL(mpam_register_requestor); > @@ -470,9 +547,37 @@ int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx, > return err; > } > > +static struct mpam_msc_ris *mpam_get_or_create_ris(struct mpam_msc *msc, > + u8 ris_idx) > +{ > + int err; > + struct mpam_msc_ris *ris, *found = ERR_PTR(-ENOENT); > + > + lockdep_assert_held(&mpam_list_lock); > + > + if (!test_bit(ris_idx, &msc->ris_idxs)) { > + err = mpam_ris_create_locked(msc, ris_idx, MPAM_CLASS_UNKNOWN, > + 0, 0); > + if (err) > + return ERR_PTR(err); > + } > + > + list_for_each_entry(ris, &msc->ris, msc_list) { > + if (ris->ris_idx == ris_idx) { > + found = ris; I'd return ris; Then can do return ERR_PTR(-ENOENT) below and not bother with found. Ignore if this gets more complex later. > + break; > + } > + } > + > + return found; > +} > @@ -675,9 +813,18 @@ static struct platform_driver mpam_msc_driver = { > > static void mpam_enable_once(void) > { > + /* > + * Once the cpuhp callbacks have been changed, mpam_partid_max can no > + * longer change. > + */ > + spin_lock(&partid_max_lock); > + partid_max_published = true; > + spin_unlock(&partid_max_lock); > + > mpam_register_cpuhp_callbacks(mpam_cpu_online, mpam_cpu_offline); > > - pr_info("MPAM enabled\n"); > + printk(KERN_INFO "MPAM enabled with %u PARTIDs and %u PMGs\n", > + mpam_partid_max + 1, mpam_pmg_max + 1); Not sure why pr_info before and printk now. > }