[PATCH 14/33] arm_mpam: Add cpuhp callbacks to probe MSC hardware

[Dave Martin]

Hi James,

While I'm here:

On Fri, Aug 22, 2025 at 03:29:55PM +0000, 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.
> 
> CC: Lecopzer Chen <lecopzerc at nvidia.com>
> Signed-off-by: James Morse <james.morse at arm.com>
> ---
>  drivers/resctrl/mpam_devices.c  | 144 +++++++++++++++++++++++++++++++-
>  drivers/resctrl/mpam_internal.h |   8 +-
>  2 files changed, 147 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 5baf2a8786fb..9d6516f98acf 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c

[...]

> @@ -511,9 +539,84 @@ 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)
> +{
> +	u64 idr;
> +	int err;

Redundant variable which gets removed again in the next patch?
 
> +
> +	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.x\n",
> +			    dev_name(&msc->pdev->dev));
> +		err = -EIO;
> +	} else {
> +		msc->probed = true;
> +		err = 0;
> +	}
> +	mutex_unlock(&msc->part_sel_lock);
> +
> +	return err;
> +}

[...]

Cheers
---Dave