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

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

[Zhiyuan Dai]

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) {
+				/* 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,
-- 
Zhiyuan Dai <daizhiyuan@phytium.com.cn>

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

[Robin Murphy]

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,