Re: [RFC PATCH 08/38] arm_mpam: resctrl: Pick the caches we will use as resctrl resources

Ben Horgan
2025-12-16T10:14:43Z

On 12/9/25 15:57, Ben Horgan wrote:
> Hi James,
>
> On 12/5/25 21:58, James Morse wrote:
>> Systems with MPAM support may have a variety of control types at any
>> point of their system layout. We can only expose certain types of
>> control, and only if they exist at particular locations.
>>
>> Start with the well-know caches. These have to be depth 2 or 3
>> and support MPAM's cache portion bitmap controls, with a number
>> of portions fewer than resctrl's limit.
>>
>> Signed-off-by: James Morse <james.morse@arm.com>
>> ---
>> drivers/resctrl/mpam_resctrl.c | 91 +++++++++++++++++++++++++++++++++-
>> 1 file changed, 89 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
>> index 320cebbd37ce..ceaf11af4fc1 100644
>> --- a/drivers/resctrl/mpam_resctrl.c
>> +++ b/drivers/resctrl/mpam_resctrl.c
>> @@ -60,10 +60,96 @@ struct rdt_resource *resctrl_arch_get_resource(enum resctrl_res_level l)
>> return &mpam_resctrl_controls[l].resctrl_res;
>> }
>>
>> +static bool cache_has_usable_cpor(struct mpam_class *class)
>> +{
>> + struct mpam_props *cprops = &class->props;
>> +
>> + if (!mpam_has_feature(mpam_feat_cpor_part, cprops))
>> + return false;
>> +
>> + /* resctrl uses u32 for all bitmap configurations */
>> + return (class->props.cpbm_wd <= 32);
>> +}
>
> cpbm_wd > 32 is not support properly in mpam_devices.c (e.g. reset and
> config value are limited to 32 bits.) and so we should consider just not
> adding the feature to the class in that case.

I'll keep this as is because the value still needs to be reset correctly
by mpam_devices.c even if it is not usable by resctrl.

>
> Thanks,
>
> Ben
>
>

Thanks,

Ben