iommu/riscv: Empty iommu queue before enabling it

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>
Link: https://lore.kernel.org/r/20250103093220.38106-2-luxu.kernel@bytedance.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: luxukernel

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