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

Ben Horgan
2026-01-19T20:48:52Z

Hi Gavin,

On 1/19/26 12:14, Gavin Shan wrote:
> 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)
>
>

That's a real error. Fixed.

Thanks,

Ben