[RFC PATCH v3 2/8] iommu/arm-smmu-v3: Add a helper to drain cmd queues

[Pranjal Shrivastava <praan@google.com>]

Before we suspend SMMU, we want to ensure that all commands have been
flushed by all the queues i.e. the queues are empty. Add a helper
function that polls till the queues are dained.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 40 +++++++++++++++++++++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  3 ++
 2 files changed, 43 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 f19a77708d2c..0df1b17a09cc 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -981,6 +981,46 @@ static int arm_smmu_cmdq_batch_submit(struct arm_smmu_device *smmu,
 					   cmds->num, true);
 }
 
+int arm_smmu_queue_poll_until_empty(struct arm_smmu_device *smmu,
+				    struct arm_smmu_queue *q)
+{
+	struct arm_smmu_queue_poll qp;
+	struct arm_smmu_ll_queue *llq = &q->llq;
+	int ret = 0;
+
+	queue_poll_init(smmu, &qp);
+	do {
+		if (queue_empty(llq))
+			break;
+
+		ret = queue_poll(&qp);
+		WRITE_ONCE(llq->cons, readl_relaxed(q->cons_reg));
+
+	} while (!ret);
+
+	return ret;
+}
+
+static int arm_smmu_drain_queues(struct arm_smmu_device *smmu)
+{
+	struct arm_smmu_cmdq *cmdq = &smmu->cmdq;
+	unsigned long flags;
+	int ret;
+
+	/*
+	 * Since this is only called from the suspend callback, we
+	 * should be able to acquire the exclusive lock without failing.
+	 */
+	arm_smmu_cmdq_exclusive_trylock_irqsave(cmdq, flags);
+	ret = arm_smmu_queue_poll_until_empty(smmu, &smmu->cmdq.q);
+	arm_smmu_cmdq_exclusive_unlock_irqrestore(cmdq, flags);
+
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
 static void arm_smmu_page_response(struct device *dev, struct iopf_fault *unused,
 				   struct iommu_page_response *resp)
 {
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index dd1ad56ce863..461f1958e574 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -965,6 +965,9 @@ int arm_smmu_init_one_queue(struct arm_smmu_device *smmu,
 int arm_smmu_cmdq_init(struct arm_smmu_device *smmu,
 		       struct arm_smmu_cmdq *cmdq);
 
+int arm_smmu_queue_poll_until_empty(struct arm_smmu_device *smmu,
+				    struct arm_smmu_queue *q);
+
 static inline bool arm_smmu_master_canwbs(struct arm_smmu_master *master)
 {
 	return dev_iommu_fwspec_get(master->dev)->flags &
-- 
2.50.0.rc2.692.g299adb8693-goog