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

[Fenghua Yu]

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.

s/return err;/return 0;/

> +}
> +
> +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