[PATCH] iommu/arm-smmu-v3: Stop queue allocation retry at PAGE_SIZE

[leo.jiang1224@foxmail.com]

From: LoserJL <leo.jiang1224@foxmail.com>

In arm_smmu_init_one_queue(), the loop reduces max_n_shift if
dmam_alloc_coherent() fails. However, since dmam_alloc_coherent()
allocates at least PAGE_SIZE, retrying with a smaller size after
a PAGE_SIZE failure is logically redundant.

Moreover, if a sub-page retry were to succeed due to concurrent memory
release, the hardware would be configured with a smaller queue depth
despite a full page being allocated. This leads to inefficient memory
usage and unnecessary hardware performance limitation.

Terminate the loop once qsz reaches PAGE_SIZE to ensure logical
consistency and optimal hardware configuration.

Signed-off-by: LoserJL <leo.jiang1224@foxmail.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

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 e8d7dbe495f0..e0ec118ff560 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4418,7 +4418,14 @@ int arm_smmu_init_one_queue(struct arm_smmu_device *smmu,
 		qsz = ((1 << q->llq.max_n_shift) * dwords) << 3;
 		q->base = dmam_alloc_coherent(smmu->dev, qsz, &q->base_dma,
 					      GFP_KERNEL);
-		if (q->base || qsz < PAGE_SIZE)
+		/*
+		 * If allocation succeeds, we're done. If it fails, only retry
+		 * if the requested size is still larger than a page. Since
+		 * dmam_alloc_coherent() allocates at least PAGE_SIZE, retrying
+		 * with a sub-page size is logically redundant and could lead
+		 * to sub-optimal hardware configuration.
+		 */
+		if (q->base || qsz <= PAGE_SIZE)
 			break;
 
 		q->llq.max_n_shift--;
-- 
2.43.0