Re: [PATCH v2] arm_mpam: Only schedule mpam_enable work after first successful MSC probe

[Ben Horgan <ben.horgan@arm.com>]

Hi Ping,

On 08/09/2026 03:48, ping.li wrote:
> From: Ping Li <leeonion.muyu@gmail.com>
> 
> mpam_discovery_cpu_online() sets new_device_probed unconditionally after
> processing each reachable MSC. Once an MSC has already been probed
> (msc->probed is true), later CPUs sharing it skip
> mpam_msc_hw_probe() but still leave err at its default value of 0.
> As a result, new_device_probed is still set to true, causing
> mpam_enable_work to be scheduled again even though no new hardware was
> probed.

This patch is an improvement but, thinking again, it looks there is scope getting rid of
mpam_enable() altogether. Rather than walking the list after each hw probe we could increment an
atomic variable, similar to what is done in mpam_msc_drv_probe(), and then just schedule
mpam_enable_once(). What do you think?

Thanks,

Ben

> 
> Set new_device_probed only when mpam_msc_hw_probe() is called and
> succeeds.
> 
> Signed-off-by: Ping Li <leeonion.muyu@gmail.com>
> ---
> Changes in v2:
> - Drop the Fixes: tag, as the extra mpam_enable() calls cause no real
>   harm: schedule_work() merges the duplicate work, and mpam_enable()
>   is a no-op until all MSCs have been probed. This is a cleanup, not a
>   bug fix.
> 
>  drivers/resctrl/mpam_devices.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 2f09f4b78bd3..fefdcf588932 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1866,13 +1866,15 @@ static int mpam_discovery_cpu_online(unsigned int cpu)
>  			continue;
>  
>  		mutex_lock(&msc->probe_lock);
> -		if (!msc->probed)
> +		if (!msc->probed) {
>  			err = mpam_msc_hw_probe(msc);
> +			if (!err)
> +				new_device_probed = true;
> +		}
>  		mutex_unlock(&msc->probe_lock);
>  
>  		if (err)
>  			break;
> -		new_device_probed = true;
>  	}
>  
>  	if (new_device_probed && !err)