Re: [PATCH v2] iommu/arm-smmu-v3: Restrict MMU-700 errata 2268618 and 2812531 to affected

[Robin Murphy <robin.murphy@arm.com>]

On 2026-02-06 8:18 am, Zhiyuan Dai wrote:
> According to SDEN-1786925, Arm errata 2268618 and 2812531 are present in
> r0p0, r0p1, and r1p0, and fixed in r1p1.
> 
> Introduce this patch to avoid performance degradation caused by
> restricting features on unaffected revisions.
> 
> Signed-off-by: Zhiyuan Dai <daizhiyuan@phytium.com.cn>
> ---
> Changelog:
> - Change the revision threshold from < 0 to < 1 to correctly.
> - Link to v1: https://lore.kernel.org/linux-iommu/3f22f7b8-449c-40d9-b4c8-fff3e520d563@arm.com/raw
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 
> 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 d16d35c78c06..d5c35be5c858 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -4272,11 +4272,13 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
>   				smmu->features &= ~ARM_SMMU_FEAT_NESTING;
>   			break;
>   		case IIDR_PRODUCTID_ARM_MMU_700:
> -			/* Arm erratum 2812531 */
> -			smmu->features &= ~ARM_SMMU_FEAT_BTM;
> -			smmu->options |= ARM_SMMU_OPT_CMDQ_FORCE_SYNC;
> -			/* Arm errata 2268618, 2812531 */
> -			smmu->features &= ~ARM_SMMU_FEAT_NESTING;
> +			if (variant <= 1 && revision < 1) {

This still breaks r0p1, and you've not addressed the other point I made...

I've now dug up the old branch where I started my own patch (back in May 
2024, yikes!), and gone through the newer errata for MMU-700 plus the 
newer MMU S3 and MMU L1 products that have also inherited some of its 
bugs - I'll finish writing up a cover letter for that and share it on 
Monday.

Thanks,
Robin.

> +				/* Arm erratum 2812531 */
> +				smmu->features &= ~ARM_SMMU_FEAT_BTM;
> +				smmu->options |= ARM_SMMU_OPT_CMDQ_FORCE_SYNC;
> +				/* Arm errata 2268618, 2812531 */
> +				smmu->features &= ~ARM_SMMU_FEAT_NESTING;
> +			}
>   			break;
>   		}
>   		break;
> 
> ---
> base-commit: b7ff7151e653aa296ab6c5495b2c1ab7c21eb250
> change-id: 20260206-smmuv3-a88772377c20
> 
> Best regards,