[PATCH] iommu/arm-smmu: Clarify MMU-500 CPRE workaround

[Robin Murphy]

On 2024-09-13 1:55 pm, Robin Murphy wrote:
> CPRE workarounds are implicated in at least 5 MMU-500 errata, some of
> which remain unfixed. The comment and warning message have proven to be
> unhelpfully misleading about this scope, so reword them to get the point
> across with less risk of going out of date or confusing users.
> 
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> ---
>   drivers/iommu/arm/arm-smmu/arm-smmu-impl.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
> index 9dc772f2cbb2..2edb1c1658ad 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
> @@ -130,7 +130,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
>   
>   	/*
>   	 * Disable MMU-500's not-particularly-beneficial next-page
> -	 * prefetcher for the sake of errata #841119 and #826419.
> +	 * prefetcher for the sake of at least 5 known errata.
>   	 */
>   	for (i = 0; i < smmu->num_context_banks; ++i) {
>   		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
> @@ -138,7 +138,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
>   		arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_ACTLR, reg);
>   		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
>   		if (reg & ARM_MMU500_ACTLR_CPRE)
> -			dev_warn_once(smmu->dev, "Failed to disable prefetcher [errata #841119 and #826419], check ACR.CACHE_LOCK\n");
> +			dev_warn_once(smmu->dev, "Failed to disable prefetcher for errata workarounds, check ACR.CACHE_LOCK\n");

Come to think of it, this should probably also refer to SACR rather than 
ACR, given that we already *have* attempted to program the Non-Secure 
side...

Robin.

>   	}
>   
>   	return 0;