linux-kernel - Re: [RFC PATCH 17/36] arm_mpam: Add cpuhp callbacks to probe MSC hardware

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Message-ID: <4da6ec99-0de5-46f1-859e-8246bc3025ff@arm.com>
Date: Wed, 6 Aug 2025 19:07:15 +0100
From: James Morse <james.morse@....com>
To: Ben Horgan <ben.horgan@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Cc: Rob Herring <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Zeng Heng
 <zengheng4@...wei.com>, Lecopzer Chen <lecopzerc@...dia.com>,
 Carl Worth <carl@...amperecomputing.com>,
 shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...amperecomputing.com>, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>
Subject: Re: [RFC PATCH 17/36] arm_mpam: Add cpuhp callbacks to probe MSC
 hardware

Hi Ben,

On 24/07/2025 15:13, Ben Horgan wrote:
> On 11/07/2025 19:36, James Morse wrote:
>> Because an MSC can only by accessed from the CPUs in its cpu-affinity
>> set we need to be running on one of those CPUs to probe the MSC
>> hardware.
>>
>> Do this work in the cpuhp callback. Probing the hardware will only
>> happen before MPAM is enabled, walk all the MSCs and probe those we can
>> reach that haven't already been probed.
>>
>> Later once MPAM is enabled, this cpuhp callback will be replaced by
>> one that avoids the global list.
>>
>> Enabling a static key will also take the cpuhp lock, so can't be done
>> from the cpuhp callback. Whenever a new MSC has been probed schedule
>> work to test if all the MSCs have now been probed.

>> diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/
>> mpam_devices.c
>> index 0d6d5180903b..89434ae3efa6 100644
>> --- a/drivers/platform/arm64/mpam/mpam_devices.c
>> +++ b/drivers/platform/arm64/mpam/mpam_devices.c
>> @@ -513,9 +541,84 @@ int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
>>       return err;
>>   }
>>   -static void mpam_discovery_complete(void)
>> +static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>   {
>> -    pr_err("Discovered all MSC\n");
>> +    u64 idr;
>> +    int err;
>> +
>> +    lockdep_assert_held(&msc->probe_lock);
>> +
>> +    mutex_lock(&msc->part_sel_lock);
>> +    idr = mpam_read_partsel_reg(msc, AIDR);
>> +    if ((idr & MPAMF_AIDR_ARCH_MAJOR_REV) != MPAM_ARCHITECTURE_V1) {
>> +        pr_err_once("%s does not match MPAM architecture v1.0\n",
>> +                dev_name(&msc->pdev->dev));

> The error message need only mention the major revision. You've added support for v1.1 and
> v1.0.

Makes sense,


Thanks,

James