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Message-ID: <44aa14c5-5b5d-421d-b486-5c63c58f0b4c@arm.com>
Date: Mon, 19 Jan 2026 20:48:45 +0000
From: Ben Horgan <ben.horgan@....com>
To: Gavin Shan <gshan@...hat.com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
baolin.wang@...ux.alibaba.com, carl@...amperecomputing.com,
dave.martin@....com, david@...nel.org, dfustini@...libre.com,
fenghuay@...dia.com, james.morse@....com, jonathan.cameron@...wei.com,
kobak@...dia.com, lcherian@...vell.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
peternewman@...gle.com, punit.agrawal@....qualcomm.com,
quic_jiles@...cinc.com, reinette.chatre@...el.com, rohit.mathew@....com,
scott@...amperecomputing.com, sdonthineni@...dia.com,
tan.shaopeng@...itsu.com, xhao@...ux.alibaba.com, catalin.marinas@....com,
will@...nel.org, corbet@....net, maz@...nel.org, oupton@...nel.org,
joey.gouly@....com, suzuki.poulose@....com, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v3 43/47] arm_mpam: Add quirk framework
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@...dia.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@...wei.com>
>> Co-developed-by: Shanker Donthineni <sdonthineni@...dia.com>
>> Signed-off-by: Shanker Donthineni <sdonthineni@...dia.com>
>> Co-developed-by: James Morse <james.morse@....com>
>> Signed-off-by: James Morse <james.morse@....com>
>> Signed-off-by: Ben Horgan <ben.horgan@....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
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