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

[Ben Horgan]

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 at arm.com> wrote:
> 
>> From: Shanker Donthineni <sdonthineni at 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 at 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 at 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