Re: [RFC PATCH 34/38] arm_mpam: Add quirk framework

Ben Horgan
2025-12-19T12:19:40Z

Hi Jonathan,

Thanks for your review. I haven't replied to every point but unless
commented I have acted on them.

On 12/18/25 14:04, Jonathan Cameron wrote:
> On Fri, 5 Dec 2025 21:58:57 +0000
> James Morse <james.morse@arm.com> 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.
>>
>> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
>> [ morse: 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 ]
>> Signed-off-by: James Morse <james.morse@arm.com>
>> ---
>> drivers/resctrl/mpam_devices.c | 27 +++++++++++++++++++++++++++
>> drivers/resctrl/mpam_internal.h | 26 ++++++++++++++++++++++++++
>> 2 files changed, 53 insertions(+)
>>
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index 741e14e1e6cf..f0f6f9b55ad4 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -630,6 +630,25 @@ 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 */
>
> Drop the trailing , given I assume whole point is nothing after this?
>
>> +};
>> +
>> +static void mpam_enable_quirks(struct mpam_msc *msc)
>> +{
>> + const struct mpam_quirk *quirk;
>> +
>> + for (quirk = &mpam_quirks[0]; quirk->iidr_mask; quirk++) {
>> + if (quirk->iidr != (msc->iidr & quirk->iidr_mask))
>> + continue;
>> +
>> + if (quirk->init)
>> + quirk->init(msc, quirk);
>
> I'm curious why you don't return a bool from this and call
> mpam_set_quirk() if that's not indicating it should not be set.
> Seems a bit odd to push the tracking that is relevant to the generic
> framework (mpam_set_quirk) down into the particular quirk inits.

Good point. I've changed the init to return 0 or an error.

>
>> + else
>> + mpam_set_quirk(quirk->workaround, msc);
>> + }
>> +}
>
>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
>> index d381906545ed..de3e5faa12b2 100644
>> --- a/drivers/resctrl/mpam_internal.h
>> +++ b/drivers/resctrl/mpam_internal.h
>> @@ -88,6 +88,8 @@ 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
>> @@ -215,6 +217,29 @@ 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,
>
> Dropping this comma should make it harder for anyone to stick an entry
> after this.

Commas removed.

Thanks,

Ben