Re: [PATCH v9 11/12] arm_mpam: change MPAM-Fb error IRQ to use a threaded IRQ handler

[Srivathsa L Rao <srivathsa.rao@oss.qualcomm.com>]

On 8/7/2026 4:24 PM, Andre Przywara wrote:
> When an MPAM MSC gets into an error condition, it can trigger an error
> IRQ. We cannot really do much about those errors, but we at least query
> and log the error, then disable MPAM functionality.
> 
> This error report relies on reading the MSC's error status register
> (ESR) in the current hard-IRQ handler, which is not possible for MPAM-Fb
> based MSC accesses, since they involve mailbox routines that might sleep.
> The same is true for clearing the interrupt at the source, which requires
> a (potentially sleeping) MSC access as well.
> 
> Change the error IRQ handler to be a threaded interrupt, but keep the
> handling in the hard-IRQ part for MMIO MSCs. This is needed since the
> CPU affinity check in the MSC accessors requires a non-preemptible
> context.
> When the MSC is using an MPAM-Fb based access, we push the work into the
> threaded part of the handler, where the accessors are allowed to sleep.
> Also forbid per-CPU interrupts (PPIs) for MPAM-Fb, as we cannot use a
> threaded IRQ here.
> 
> The actual IRQ handler learns how to deal with errors. We cannot really
> handle them, but we can try our best to disable the IRQ anyway.
> Should the level IRQ line deactivation fail on the device side, we mask
> the IRQ on the irqchip level, to prevent an interrupt storm.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>   drivers/resctrl/mpam_devices.c | 77 ++++++++++++++++++++++++++++------
>   1 file changed, 65 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index fb2fba5ba96d..4b1382fce2be 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
Reviewed-by: Srivathsa L Rao <srivathsa.rao@oss.qualcomm.com>