Re: [PATCH v3 43/47] arm_mpam: Add quirk framework

Gavin Shan
2026-01-19T12:15:00Z

On 1/13/26 12:59 AM, Ben Horgan wrote:
> From: Shanker Donthineni <sdonthineni@nvidia.com>
>
> The MPAM specification includes the MPAMF_IIDR, which serves to uniquely
> identify the MSC implementation through a combination of implementer
> details, product ID, variant, and revision. Certain hardware issues/errata
> can be resolved using software workarounds.
>
> Introduce a quirk framework to allow workarounds to be enabled based on the
> MPAMF_IIDR value.
>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Co-developed-by: Shanker Donthineni <sdonthineni@nvidia.com>
> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
> Co-developed-by: James Morse <james.morse@arm.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
> Changes by James:
> Stash the IIDR so this doesn't need an IPI, enable quirks only
> once, move the description to the callback so it can be pr_once()d, add an
> enum of workarounds for popular errata. Add macros for making lists of
> product/revision/vendor half readable
>
> Changes since rfc:
> remove trailing commas in last element of enums
> Make mpam_enable_quirks() in charge of mpam_set_quirk() even if there
> is an enable.
> ---
> drivers/resctrl/mpam_devices.c | 32 ++++++++++++++++++++++++++++++++
> drivers/resctrl/mpam_internal.h | 25 +++++++++++++++++++++++++
> 2 files changed, 57 insertions(+)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 37bd8efc6ecf..5f741df9abcc 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -630,6 +630,30 @@ static struct mpam_msc_ris *mpam_get_or_create_ris(struct mpam_msc *msc,
> return ERR_PTR(-ENOENT);
> }
>
> +static const struct mpam_quirk mpam_quirks[] = {
> + { NULL } /* Sentinel */
> +};
> +
> +static void mpam_enable_quirks(struct mpam_msc *msc)
> +{
> + const struct mpam_quirk *quirk;
> +
> + for (quirk = &mpam_quirks[0]; quirk->iidr_mask; quirk++) {
> + int err = 0;
> +
> + if (quirk->iidr != (msc->iidr & quirk->iidr_mask))
> + continue;
> +
> + if (quirk->init)
> + err = quirk->init(msc, quirk);
> +
> + if (err)
> + continue;
> +
> + mpam_set_quirk(quirk->workaround, msc);
> + }
> +}
> +
> /*
> * IHI009A.a has this nugget: "If a monitor does not support automatic behaviour
> * of NRDY, software can use this bit for any purpose" - so hardware might not
> @@ -864,8 +888,11 @@ 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);
> idr = mpam_msc_read_idr(msc);
> + msc->iidr = mpam_read_partsel_reg(msc, IIDR);
> mutex_unlock(&msc->part_sel_lock);
>
> + mpam_enable_quirks(msc);
> +
> msc->ris_max = FIELD_GET(MPAMF_IDR_RIS_MAX, idr);
>
> /* Use these values so partid/pmg always starts with a valid value */
> @@ -1993,6 +2020,7 @@ static bool mpam_has_cmax_wd_feature(struct mpam_props *props)
> * resulting safe value must be compatible with both. When merging values in
> * the tree, all the aliasing resources must be handled first.
> * On mismatch, parent is modified.
> + * Quirks on an MSC will apply to all MSC in that class.
> */
> static void __props_mismatch(struct mpam_props *parent,
> struct mpam_props *child, bool alias)
> @@ -2112,6 +2140,7 @@ static void __props_mismatch(struct mpam_props *parent,
> * nobble the class feature, as we can't configure all the resources.
> * e.g. The L3 cache is composed of two resources with 13 and 17 portion
> * bitmaps respectively.
> + * Quirks on an MSC will apply to all MSC in that class.
> */
> static void
> __class_props_mismatch(struct mpam_class *class, struct mpam_vmsc *vmsc)
> @@ -2125,6 +2154,9 @@ __class_props_mismatch(struct mpam_class *class, struct mpam_vmsc *vmsc)
> dev_dbg(dev, "Merging features for class:0x%lx &= vmsc:0x%lx\n",
> (long)cprops->features, (long)vprops->features);
>
> + /* Merge quirks */
> + class->quirks |= vmsc->msc->quirks;
> +
> /* Take the safe value for any common features */
> __props_mismatch(cprops, vprops, false);
> }
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 69cb75616561..d60a3caf6f6e 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -85,6 +85,8 @@ struct mpam_msc {
> u8 pmg_max;
> unsigned long ris_idxs;
> u32 ris_max;
> + u32 iidr;
> + u16 quirks;
>
> /*
> * error_irq_lock is taken when registering/unregistering the error
> @@ -216,6 +218,28 @@ struct mpam_props {
> #define mpam_set_feature(_feat, x) __set_bit(_feat, (x)->features)
> #define mpam_clear_feature(_feat, x) __clear_bit(_feat, (x)->features)
>
> +/* Workaround bits for msc->quirks */
> +enum mpam_device_quirks {
> + MPAM_QUIRK_LAST
> +};
> +
> +#define mpam_has_quirk(_quirk, x) ((1 << (_quirk) & (x)->quirks))
> +#define mpam_set_quirk(_quirk, x) ((x)->quirks |= (1 << (_quirk)))
> +
> +struct mpam_quirk {
> + int (*init)(struct mpam_msc *msc, const struct mpam_quirk *quirk);
> +
> + u32 iidr;
> + u32 iidr_mask;
> +
> + enum mpam_device_quirks workaround;
> +};
> +
> +#define MPAM_IIDR_MATCH_ONE FIELD_PREP_CONST(MPAMF_IIDR_PRODUCTID, 0xfff) | \
> + FIELD_PREP_CONST(MPAMF_IIDR_VARIANT, 0xf) | \
> + FIELD_PREP_CONST(MPAMF_IIDR_REVISION, 0xf) | \
> + FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0xfff)
> +

An error reported by checkpatch.pl as below.

ERROR: Macros with complex values should be enclosed in parentheses
#135: FILE: drivers/resctrl/mpam_internal.h:238:
+#define MPAM_IIDR_MATCH_ONE FIELD_PREP_CONST(MPAMF_IIDR_PRODUCTID, 0xfff) | \
+ FIELD_PREP_CONST(MPAMF_IIDR_VARIANT, 0xf) | \
+ FIELD_PREP_CONST(MPAMF_IIDR_REVISION, 0xf) | \
+ FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0xfff)

> /* The values for MSMON_CFG_MBWU_FLT.RWBW */
> enum mon_filter_options {
> COUNT_BOTH = 0,
> @@ -259,6 +283,7 @@ struct mpam_class {
>
> struct mpam_props props;
> u32 nrdy_usec;
> + u16 quirks;
> u8 level;
> enum mpam_class_types type;
>

Thanks,
Gavin