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

[Jonathan Cameron]

On Fri, 11 Jul 2025 18:36:29 +0000
James Morse <james.morse at arm.com> 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.
> 
> CC: Lecopzer Chen <lecopzerc at nvidia.com>
> Signed-off-by: James Morse <james.morse at arm.com>
Hi James,

One trivial thing noticed whilst testing..

> @@ -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",
You are only checking MAJOR REV which is probably the right thing to do
but in that case maybe change the message to be v1.x ?

> +			    dev_name(&msc->pdev->dev));
> +		err = -EIO;
> +	} else {
> +		msc->probed = true;
> +		err = 0;
> +	}
> +	mutex_unlock(&msc->part_sel_lock);
> +
> +	return err;
> +}
> +