[PATCH v3] xen/arm: smmuv3: mark arm_smmu_disable_pasid __maybe_unused

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

When building with clang 12 and CONFIG_ARM_SMMU_V3=y, we observe the
following build error:

drivers/passthrough/arm/smmu-v3.c:1408:20: error: unused function 
'arm_smmu_disable_pasid' [-Werror,-Wunused-function]
static inline void arm_smmu_disable_pasid(struct arm_smmu_master *master) { }
                   ^

arm_smmu_disable_pasid is not currently called from anywhere in Xen, but
it is inside a section of code guarded by CONFIG_PCI_ATS, which may be
helpful in the future if the PASID feature is to be implemented. Add the
attribute __maybe_unused to the function.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
Reviewed-by: Rahul Singh <rahul.singh@xxxxxxx>
---
v2->v3:
Place __maybe_unused after "void" and add newline after __maybe_unused
Add Rahul's R-b

v1->v2:
Add __maybe_unused attribute instead of removing
---
 xen/drivers/passthrough/arm/smmu-v3.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu-v3.c 
b/xen/drivers/passthrough/arm/smmu-v3.c
index 9c9f4630090e..d58c5cd0bf77 100644
--- a/xen/drivers/passthrough/arm/smmu-v3.c
+++ b/xen/drivers/passthrough/arm/smmu-v3.c
@@ -1376,7 +1376,8 @@ static int arm_smmu_enable_pasid(struct arm_smmu_master 
*master)
        return 0;
 }
 
-static void arm_smmu_disable_pasid(struct arm_smmu_master *master)
+static void __maybe_unused
+arm_smmu_disable_pasid(struct arm_smmu_master *master)
 {
        struct pci_dev *pdev;
 
@@ -1405,7 +1406,8 @@ static inline int arm_smmu_enable_pasid(struct 
arm_smmu_master *master)
        return 0;
 }
 
-static inline void arm_smmu_disable_pasid(struct arm_smmu_master *master) { }
+static inline void __maybe_unused
+arm_smmu_disable_pasid(struct arm_smmu_master *master) { }
 #endif /* CONFIG_PCI_ATS */
 
 static void arm_smmu_detach_dev(struct arm_smmu_master *master)
-- 
2.39.0