[PATCH] vdpa/ifc/base: wait for queue disable before saving q-state

[Abhishek Maheshwari <abhishek.maheshwari@intel.com>]

Some ifc hardware require synchronization between disabling a queue and
saving queue-state from LM registers. When queue is disabled from vDPA
driver, ifc device stops executing new virtio-cmds and then updates LM
registers with used/avail index. Before saving the queue-state, vDPA
driver should wait until the queue is disabled from backend.

Signed-off-by: Abhishek Maheshwari <abhishek.maheshwari@intel.com>
---
 drivers/vdpa/ifc/base/ifcvf.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/vdpa/ifc/base/ifcvf.c b/drivers/vdpa/ifc/base/ifcvf.c
index f1e1474447..fb51c793a2 100644
--- a/drivers/vdpa/ifc/base/ifcvf.c
+++ b/drivers/vdpa/ifc/base/ifcvf.c
@@ -257,6 +257,7 @@ ifcvf_hw_disable(struct ifcvf_hw *hw)
 	u32 i;
 	struct ifcvf_pci_common_cfg *cfg;
 	u32 ring_state;
+	int q_disable_tries;
 
 	cfg = hw->common_cfg;
 	if (!cfg) {
@@ -275,6 +276,20 @@ ifcvf_hw_disable(struct ifcvf_hw *hw)
 			continue;
 		}
 
+        /* Some ifc hardware require synchronization between disabling a queue
+         * and saving queue-state from LM registers.
+         * When queue is disabled from vDPA driver, ifc device stops executing
+         * new virtio-cmds and then updates LM registers with used/avail index.
+         * Before saving the queue-state, vDPA driver waits until the queue is
+         * disabled from backend.
+		 */
+		q_disable_tries = 10;
+		while (q_disable_tries-- && IFCVF_READ_REG16(&cfg->queue_enable))
+			msec_delay(10);
+
+		if (IFCVF_READ_REG16(&cfg->queue_enable))
+			WARNINGOUT("Failed Q disable: %d. saved state is invalid\n", i);
+
 		if (hw->device_type == IFCVF_BLK)
 			ring_state = *(u32 *)(hw->lm_cfg +
 					IFCVF_LM_RING_STATE_OFFSET +
-- 
2.31.1