Re: [PATCH v6 09/10] arm_mpam: change MPAM-Fb error IRQ to use a threaded IRQ handler

[Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>]

On Thu, 30 Jul 2026 17:25:38 +0200
Andre Przywara <andre.przywara@arm.com> 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
> an MSC access as well.
> 
> When an MSC is using MPAM-Fb, change the error IRQ to use a threaded IRQ
> handler, with an empty hard IRQ routine, and doing all the MSC accesses
> (to access the status and disable the IRQ line) in the threaded part.
> The change is minimal, we just check for the first MSC access error and
> bail out early. MMIO based MSCs keep using a hard-IRQ handler, since
> they must be at least non-migrate-able when doing MSC accesses, for the
> CPU affinity check to work.
> Also forbid per-CPU interrupts (PPIs) for MPAM-Fb, as we cannot use a
> threaded IRQ here.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>

One thing below.

> ---
>  drivers/resctrl/mpam_devices.c | 64 ++++++++++++++++++++++++++--------
>  1 file changed, 49 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index daaf3cf48475..606ae4af2be9 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c

> @@ -2747,9 +2766,24 @@ static int mpam_register_irqs(void)
>  					       &_enable_percpu_irq, &irq,
>  					       true);
>  		} else {
> -			err = devm_request_irq(&msc->pdev->dev, irq,
> -					       &mpam_spi_handler, IRQF_SHARED,
> -					       "mpam:msc:error", msc);
> +			irq_handler_t hard, threaded;
> +
> +			/*
> +			 * MPAM-Fb needs a sleepable context for the MSC
> +			 * accesses, whereas MMIO requires at least a
> +			 * non-migrateable context for the processor ID check.
> +			 */
> +			if (msc->iface == MPAM_IFACE_MMIO) {
> +				hard = &mpam_spi_handler;
> +				threaded = NULL;
> +			} else {
> +				hard = NULL;
> +				threaded = &mpam_spi_handler;
> +			}
> +			err = devm_request_threaded_irq(&msc->pdev->dev, irq,
> +							hard, threaded,
> +							IRQF_SHARED | IRQF_ONESHOT,

IIRC correctly you'll trip a warning message for the case of MMIO and marking
it as IRQF_ONESHOT. See __setup_irq()

That was a fairly recent check to be added and caused all sorts of problems
with cases similar to this one where the handlers are coming from variables.

Upshot, you need to call appropriate registration function.


Jonathan




> +							"mpam:msc:error", msc);
>  			if (err)
>  				return err;
>  		}