Subject: Re: [PATCH] iommu/arm-smmu: Report USF more clearly

From: Robin Murphy <[email-masked]>
Date: Fri, 13 Sep 2019 15:34:16 +0100

On 13/09/2019 12:48, Robin Murphy wrote:
> Although CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT is a welcome tool
> for smoking out inadequate firmware, the failure mode is non-obvious
> and can be confusing for end users. Add some special-case reporting of
> Unidentified Stream Faults to help clarify this particular symptom.
> 
> CC: Douglas Anderson <[email-masked]>
> Signed-off-by: Robin Murphy <[email-masked]>
> ---
>   drivers/iommu/arm-smmu.c | 5 +++++
>   drivers/iommu/arm-smmu.h | 2 ++
>   2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index b7cf24402a94..76ac8c180695 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -499,6 +499,11 @@ static irqreturn_t arm_smmu_global_fault(int irq, void *dev)
>   	dev_err_ratelimited(smmu->dev,
>   		"\tGFSR 0x%08x, GFSYNR0 0x%08x, GFSYNR1 0x%08x, GFSYNR2 0x%08x\n",
>   		gfsr, gfsynr0, gfsynr1, gfsynr2);
> +	if (IS_ENABLED(CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT) &&
> +	    (gfsr & sGFSR_USF))
> +		dev_err_ratelimited(smmu->dev,
> +			"Stream ID %hu may not be described by firmware, try booting with \"arm-smmu.disable_bypass=0\"\n",
> +			(u16)gfsynr1);
>   
>   	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_sGFSR, gfsr);
>   	return IRQ_HANDLED;
> diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> index c9c13b5785f2..46f7e161e83e 100644
> --- a/drivers/iommu/arm-smmu.h
> +++ b/drivers/iommu/arm-smmu.h
> @@ -79,6 +79,8 @@
>   #define ID7_MINOR			GENMASK(3, 0)
>   
>   #define ARM_SMMU_GR0_sGFSR		0x48
> +#define sGFSR_USF			BIT(2)

Sigh... and of course what I actually meant here was that this is the 
2nd bit, which is bit 1, which is also 2. I blame Friday :(

Robin.

> +
>   #define ARM_SMMU_GR0_sGFSYNR0		0x50
>   #define ARM_SMMU_GR0_sGFSYNR1		0x54
>   #define ARM_SMMU_GR0_sGFSYNR2		0x58
> 

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