[PATCH v3 07/29] arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate

[Tushar Dave]

On 10/21/25 7:29 PM, Fenghua Yu wrote:
> Hi, James,
> 
> On 10/17/25 11:56, James Morse wrote:
>> Probing MPAM is convoluted. MSCs that are integrated with a CPU may
>> only be accessible from those CPUs, and they may not be online.
>> Touching the hardware early is pointless as MPAM can't be used until
>> the system-wide common values for num_partid and num_pmg have been
>> discovered.
>>
>> Start with driver probe/remove and mapping the MSC.
>>
>> CC: Carl Worth <carl at os.amperecomputing.com>
>> Tested-by: Fenghua Yu <fenghuay at nvidia.com>
>> Signed-off-by: James Morse <james.morse at arm.com>
> [SNIP]> +/*
>> + * An MSC can control traffic from a set of CPUs, but may only be accessible
>> + * from a (hopefully wider) set of CPUs. The common reason for this is power
>> + * management. If all the CPUs in a cluster are in PSCI:CPU_SUSPEND, the
>> + * corresponding cache may also be powered off. By making accesses from
>> + * one of those CPUs, we ensure this isn't the case.
>> + */
>> +static int update_msc_accessibility(struct mpam_msc *msc)
>> +{
>> +    u32 affinity_id;
>> +    int err;
>> +
>> +    err = device_property_read_u32(&msc->pdev->dev, "cpu_affinity",
>> +                       &affinity_id);
>> +    if (err)
>> +        cpumask_copy(&msc->accessibility, cpu_possible_mask);
>> +    else
>> +        acpi_pptt_get_cpus_from_container(affinity_id,
>> +                          &msc->accessibility);
>> +    return err;
> 
> The error is handled and there is no need to return the error to caller.
> Returning the error causes probe failure and the mpam_msc driver cannot be 
> installed.

Ack. I see the probe failure too.

e.g.

[    7.118297] mpam_msc mpam_msc.183: probe with driver mpam_msc failed with 
error -22
[    7.118383] mpam_msc mpam_msc.370: probe with driver mpam_msc failed with 
error -22
[   10.208127]     # Subtest: mpam_devices_test_suite
[   10.208129]     # module: mpam
[   10.208215]     ok 1 test_mpam_reset_msc_bitmap
[   10.208275] mpam:__props_mismatch: __props_mismatch took the min cmax_wd
[   10.208285] mpam:__props_mismatch: cleared cpor_part
[   10.208287] mpam:__props_mismatch: cleared mbw_part
[   10.208294] mpam:__props_mismatch: took the min bwa_wd
[   10.208296] mpam:__props_mismatch: __props_mismatch took the min cmax_wd
[   10.208310] mpam:__props_mismatch: __props_mismatch took the min cmax_wd
[   10.208345]     ok 2 test_mpam_enable_merge_features
[   10.208411] # mpam_devices_test_suite: pass:3 fail:0 skip:0 total:3
[   10.208413] ok 1 mpam_devices_test_suite

> 
> s/return err;/return 0;/

Yes, this resolve the probe failure.

Tested-by: Tushar Dave <tdave at nvidia.com>

> 
>> +}
>> +
>> +static int fw_num_msc;
>> +
>> +static void mpam_msc_destroy(struct mpam_msc *msc)
>> +{
>> +    struct platform_device *pdev = msc->pdev;
>> +
>> +    lockdep_assert_held(&mpam_list_lock);
>> +
>> +    list_del_rcu(&msc->all_msc_list);
>> +    platform_set_drvdata(pdev, NULL);
>> +}
>> +
>> +static void mpam_msc_drv_remove(struct platform_device *pdev)
>> +{
>> +    struct mpam_msc *msc = platform_get_drvdata(pdev);
>> +
>> +    if (!msc)
>> +        return;
>> +
>> +    mutex_lock(&mpam_list_lock);
>> +    mpam_msc_destroy(msc);
>> +    mutex_unlock(&mpam_list_lock);
>> +
>> +    synchronize_srcu(&mpam_srcu);
>> +}
>> +
>> +static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
>> +{
>> +    int err;
>> +    u32 tmp;
>> +    struct mpam_msc *msc;
>> +    struct resource *msc_res;
>> +    struct device *dev = &pdev->dev;
>> +
>> +    lockdep_assert_held(&mpam_list_lock);
>> +
>> +    msc = devm_kzalloc(&pdev->dev, sizeof(*msc), GFP_KERNEL);
>> +    if (!msc)
>> +        return ERR_PTR(-ENOMEM);
>> +
>> +    mutex_init(&msc->probe_lock);
>> +    mutex_init(&msc->part_sel_lock);
>> +    msc->id = pdev->id;
>> +    msc->pdev = pdev;
>> +    INIT_LIST_HEAD_RCU(&msc->all_msc_list);
>> +    INIT_LIST_HEAD_RCU(&msc->ris);
>> +
>> +    err = update_msc_accessibility(msc);
>> +    if (err)
>> +        return ERR_PTR(err);
> 
> The returned error causes probe failure and the driver cannot be installed. 
> Return 0 will make the probe succeed.
> 
> There is no probe failure in mpam/snapshot/v6.18-rc1 because its returned err=0.
> 
> [SNIP]
> 
> Thanks.
> 
> -Fenghua
>