[PATCH RESEND 1/2] iommu/riscv: Empty iommu queue before enabling it

[Xu Lu <luxu.kernel@bytedance.com>]

Changing cqen/fqen/pqen from 0 to 1 sets the cqh/fqt/pqt registers to 0.
But the cqt/fqh/pqh registers are left unmodified. This commit resets
cqt/fqh/pqh registers to ensure corresponding queues are empty before
being enabled during initialization.

Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
---
 drivers/iommu/riscv/iommu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index 8a05def774bd..84806724f568 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -240,6 +240,12 @@ static int riscv_iommu_queue_enable(struct riscv_iommu_device *iommu,
 		return rc;
 	}
 
+	/* Empty queue before enabling it */
+	if (queue->qid == RISCV_IOMMU_INTR_CQ)
+		riscv_iommu_writel(queue->iommu, Q_TAIL(queue), 0);
+	else
+		riscv_iommu_writel(queue->iommu, Q_HEAD(queue), 0);
+
 	/*
 	 * Enable queue with interrupts, clear any memory fault if any.
 	 * Wait for the hardware to acknowledge request and activate queue
-- 
2.20.1