Re: [PATCH] iommu/arm-smmu-v3: Disable PRI when no priq IRQ is available

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Jun 22, 2026 at 09:17:03AM -0700, Breno Leitao wrote:
> When platform firmware advertises an SMMU as PRI-capable in IDR0.PRI
> but does not assign a GSIV for its priq, arm_smmu_setup_unique_irqs()
> warns and continues. ARM_SMMU_FEAT_PRI remains set, so the driver
> still allocates the PRI queue, programs PRIQ_BASE/PROD/CONS, enables
> IRQ_CTRL_PRIQ_IRQEN, and lets IOMMU_DEV_FEAT_IOPF be advertised to
> upper layers. Page Request messages from devices land in a queue no
> one drains, and SVA binds appear to succeed while silently dropping
> every page fault.
> 
> Clear ARM_SMMU_FEAT_PRI in the missing-IRQ path so every PRI-gated
> site in the driver consistently treats the SMMU as PRI-less, instead of
> the half-baked stated.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index a10affb483a4f..44bafbb38e242 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -4659,7 +4659,8 @@ static void arm_smmu_setup_unique_irqs(struct arm_smmu_device *smmu)
>  				dev_warn(smmu->dev,
>  					 "failed to enable priq irq\n");
>  		} else {
> -			dev_warn(smmu->dev, "no priq irq - PRI will be broken\n");
> +			dev_warn(smmu->dev, "no priq irq - disabling PRI\n");
> +			smmu->features &= ~ARM_SMMU_FEAT_PRI;

This is covered by PATCH-7 in my PRI series:
https://lore.kernel.org/linux-iommu/cover.1779944354.git.nicolinc@nvidia.com/

FWIW, changing arm_smmu_setup_unique_irqs() alone isn't complete,
as Sashiko pointed it out:
https://sashiko.dev/#/patchset/20260622-smmu_pri-v1-1-14ad92b6043f%40debian.org

Nicolin