[PATCH 0/2] iommu/arm-smmu: Use FIELD_MODIFY() for bitfield operations

[PATCH 0/2] iommu/arm-smmu: Use FIELD_MODIFY() for bitfield operations

[Hans Zhang]

Replace open-coded bitfield modifications with the standard FIELD_MODIFY()
macro. This improves code readability and adds type/range checking without
functional changes.

FIELD_MODIFY() internally performs the same mask-clear + set operation but
eliminates repetitive boilerplate.

---
Hi, If the Maintainers think it's not necessary, please ignore it.
---

Hans Zhang (2):
  iommu/arm-smmu-qcom: Use FIELD_MODIFY()
  iommu/arm-smmu-v3: Use FIELD_MODIFY()

 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 5 ++---
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c    | 3 +--
 2 files changed, 3 insertions(+), 5 deletions(-)


base-commit: 3b3bea6d4b9c162f9e555905d96b8c1da67ecd5b
-- 
2.34.1

[PATCH 1/2] iommu/arm-smmu-qcom: Use FIELD_MODIFY()

[Hans Zhang]

Use FIELD_MODIFY() to remove open-coded bit manipulation.
No functional change intended.

Signed-off-by: Hans Zhang <18255117159@163.com>
---
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c
index 65e0ef6539fe..99469c4ebac2 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c
@@ -208,8 +208,7 @@ static phys_addr_t qcom_tbu_trigger_atos(struct arm_smmu_domain *smmu_domain,
 
 	/* Set address and stream-id */
 	val = readq_relaxed(tbu->base + DEBUG_SID_HALT_REG);
-	val &= ~DEBUG_SID_HALT_SID;
-	val |= FIELD_PREP(DEBUG_SID_HALT_SID, sid);
+	FIELD_MODIFY(DEBUG_SID_HALT_SID, &val, sid);
 	writeq_relaxed(val, tbu->base + DEBUG_SID_HALT_REG);
 	writeq_relaxed(iova, tbu->base + DEBUG_VA_ADDR_REG);
 	val = FIELD_PREP(DEBUG_AXUSER_CDMID, DEBUG_AXUSER_CDMID_VAL);
-- 
2.34.1

[PATCH 2/2] iommu/arm-smmu-v3: Use FIELD_MODIFY()

[Hans Zhang]

Use FIELD_MODIFY() to remove open-coded bit manipulation.
No functional change intended.

Signed-off-by: Hans Zhang <18255117159@163.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
index ddae0b07c76b..b62e91e4781d 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
@@ -330,8 +330,7 @@ static int arm_vsmmu_convert_user_cmd(struct arm_vsmmu *vsmmu,
 	case CMDQ_OP_TLBI_NH_VAA:
 	case CMDQ_OP_TLBI_NH_ALL:
 	case CMDQ_OP_TLBI_NH_ASID:
-		cmd->cmd[0] &= ~CMDQ_TLBI_0_VMID;
-		cmd->cmd[0] |= FIELD_PREP(CMDQ_TLBI_0_VMID, vsmmu->vmid);
+		FIELD_MODIFY(CMDQ_TLBI_0_VMID, &cmd->cmd[0], vsmmu->vmid);
 		break;
 	case CMDQ_OP_ATC_INV:
 	case CMDQ_OP_CFGI_CD:
@@ -340,8 +339,7 @@ static int arm_vsmmu_convert_user_cmd(struct arm_vsmmu *vsmmu,
 
 		if (arm_vsmmu_vsid_to_sid(vsmmu, vsid, &sid))
 			return -EIO;
-		cmd->cmd[0] &= ~CMDQ_CFGI_0_SID;
-		cmd->cmd[0] |= FIELD_PREP(CMDQ_CFGI_0_SID, sid);
+		FIELD_MODIFY(CMDQ_CFGI_0_SID, &cmd->cmd[0], sid);
 		break;
 	}
 	default:
-- 
2.34.1

Re: [PATCH 0/2] iommu/arm-smmu: Use FIELD_MODIFY() for bitfield operations

[Will Deacon]

On Fri, May 01, 2026 at 12:45:43AM +0800, Hans Zhang wrote:
> Replace open-coded bitfield modifications with the standard FIELD_MODIFY()
> macro. This improves code readability and adds type/range checking without
> functional changes.

Does it _really_ improve the readability? '&=' and '|=' patterns are
pretty idiomatic C code, if you ask me.

> FIELD_MODIFY() internally performs the same mask-clear + set operation but
> eliminates repetitive boilerplate.
> 
> ---
> Hi, If the Maintainers think it's not necessary, please ignore it.

I don't really mind the code either way, so I think I'd prefer to leave
it as-is unless somebody wants to convince me otherwise...

Will

Re: [PATCH 0/2] iommu/arm-smmu: Use FIELD_MODIFY() for bitfield operations

[Hans Zhang]

On 5/19/26 18:51, Will Deacon wrote:
> On Fri, May 01, 2026 at 12:45:43AM +0800, Hans Zhang wrote:
>> Replace open-coded bitfield modifications with the standard FIELD_MODIFY()
>> macro. This improves code readability and adds type/range checking without
>> functional changes.
> 
> Does it _really_ improve the readability? '&=' and '|=' patterns are
> pretty idiomatic C code, if you ask me.
> 
>> FIELD_MODIFY() internally performs the same mask-clear + set operation but
>> eliminates repetitive boilerplate.
>>
>> ---
>> Hi, If the Maintainers think it's not necessary, please ignore it.
> 
> I don't really mind the code either way, so I think I'd prefer to leave
> it as-is unless somebody wants to convince me otherwise...
> 
> Will

Hi Will,

It's not like that. Please take a look at the accepted patch below.



https://lore.kernel.org/linux-pci/20260505165436.GA737933@bhelgaas/

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=42ec65b46a4fc7565d48daa42bf025fdc67800eb

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=5fd6f2154734f447e83b6de9a08d16848605191e


Best regards,
Hans