[RFC PATCH 2/5] iommu/arm-smmu-v3: Add a helper to wait till cmdq drains

[Pranjal Shrivastava <praan@google.com>]

Before we suspend SMMU, we want to ensure that all commands have been
consumed by the SMMU's command queue, i.e. the cmdq is empty. Add a
helper function that waits till the cmdq is empty using `queue_empty`.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 24 +++++++++++++++++++++
 1 file changed, 24 insertions(+)

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 80362d9f293b..f65d9bca0392 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -754,6 +754,30 @@ static int arm_smmu_cmdq_poll_until_sync(struct arm_smmu_device *smmu,
 	return __arm_smmu_cmdq_poll_until_consumed(smmu, cmdq, llq);
 }
 
+/*
+ * Wait until the SMMU cmdq is empty
+ * Must be called with the cmdq lock held in some capacity.
+ */
+static int arm_smmu_cmdq_poll_until_empty(struct arm_smmu_device *smmu,
+					  struct arm_smmu_cmdq *cmdq,
+					  struct arm_smmu_ll_queue *llq)
+{
+	struct arm_smmu_queue_poll qp;
+	int ret = 0;
+
+	queue_poll_init(smmu, &qp);
+	llq->val = READ_ONCE(cmdq->q.llq.val);
+	do {
+		if (queue_empty(llq))
+			break;
+
+		ret = queue_poll(&qp);
+		llq->cons = readl(cmdq->q.cons_reg);
+	} while (!ret);
+
+	return ret;
+}
+
 static void arm_smmu_cmdq_write_entries(struct arm_smmu_cmdq *cmdq, u64 *cmds,
 					u32 prod, int n)
 {
-- 
2.49.0.rc1.451.g8f38331e32-goog