[PATCH] iommu/arm-smmu-v3: Warn about missing IRQs

[will.deacon@arm.com (Will Deacon)]

On Fri, Oct 27, 2017 at 02:08:16PM +0100, Robin Murphy wrote:
> It is annoyingly non-obvious when DMA transactions silently go missing
> due to undetected SMMU faults. Help skip the first few debugging steps
> in those situations by making it clear when we have neither wired IRQs
> nor MSIs with which to raise error conditions.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/arm-smmu-v3.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index e67ba6c40faf..1a374c5c9507 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -2263,6 +2263,8 @@ static void arm_smmu_setup_unique_irqs(struct arm_smmu_device *smmu)
>  						"arm-smmu-v3-evtq", smmu);
>  		if (ret < 0)
>  			dev_warn(smmu->dev, "failed to enable evtq irq\n");
> +	} else {
> +		dev_warn(smmu->dev, "no evtq irq - events will not be reported!\n");
>  	}
>  
>  	irq = smmu->cmdq.q.irq;
> @@ -2280,6 +2282,8 @@ static void arm_smmu_setup_unique_irqs(struct arm_smmu_device *smmu)
>  				       0, "arm-smmu-v3-gerror", smmu);
>  		if (ret < 0)
>  			dev_warn(smmu->dev, "failed to enable gerror irq\n");
> +	} else {
> +		dev_warn(smmu->dev, "no gerr irq - errors will not be reported!\n");
>  	}
>  
>  	if (smmu->features & ARM_SMMU_FEAT_PRI) {

Can we also print something similar for the PRIQ when we detect that PRI is
supported, please? Whilst I agree that event and gerror are the critical
ones, I'm not sure how a PCIe device behaves if its PRI requests are
ignored, but this might help to debug it.

Will