Re: [PATCH v2 02/12] arm_mpam: Restore the error interrupt enable from mpam_cpu_online()

[James Morse <james.morse@arm.com>]

Hi Ben,

On 17/09/2026 15:56, Ben Horgan wrote:
> When all the associated CPUs to an MSC are offline, possibly caused by
> PSCI_CPU_OFF, the power supply to the MSC can be cut off and all the
> registers that are unknown out of reset, including MPAMF_ECR.INTEN, are
> lost.

Surely all the registers lose their value - and what we get back is the
architecture's reset values. MPAMF_ECR doesn't seem to have one, we can assume
its UNKNOWN.

(I've rephrased this)


> Afterwards, we need to explicitly set MPAMF_ECR.INTEN when the first
> associated CPU becomes online and the power supply to the MSC is recovered.
> 
> Restore MPAMF_ECR.INTEN in mpam_cpu_online() when the first associated CPU
> of the MSC becomes online.

You won't be surprised to know I didn't have a platform that generated interrupts
when this was written!


> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 580d7ed38569..32bde94dfbc3 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1856,8 +1856,14 @@ static int mpam_cpu_online(unsigned int cpu)
>  		if (msc->reenable_error_ppi)
>  			_enable_percpu_irq(&msc->reenable_error_ppi);
>  
> -		if (atomic_fetch_inc(&msc->online_refs) == 0)
> +		if (atomic_fetch_inc(&msc->online_refs) == 0) {
> +			mutex_lock(&msc->error_irq_lock);
> +			if (msc->error_irq_hw_enabled)
> +				mpam_touch_msc(msc, mpam_enable_msc_ecr, msc);
> +			mutex_unlock(&msc->error_irq_lock);
> +
>  			mpam_reprogram_msc(msc);
> +		}
>  	}
>  
>  	if (mpam_resctrl_enabled)


Reviewed-by: James Morse <james.morse@arm.com>


Thanks,

James