RE: [PATCH v5] vdpa/ifc/base: wait for queue disable before saving q-state

["Mandal, Purna Chandra" <purna.chandra.mandal@intel.com>]

-----Original Message-----
From: Maheshwari, Abhishek <abhishek.maheshwari@intel.com> 
Sent: Thursday, November 3, 2022 3:05 PM
To: maxime.coquelin@redhat.com; Wang, Xiao W <xiao.w.wang@intel.com>
Cc: dev@dpdk.org; stable@dpdk.org; Xia, Chenbo <chenbo.xia@intel.com>; Mandal, Purna Chandra <purna.chandra.mandal@intel.com>; Maheshwari, Abhishek <abhishek.maheshwari@intel.com>
Subject: [PATCH v5] vdpa/ifc/base: wait for queue disable before saving q-state

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.

Fixes: 5d75517beffe ("vdpa/ifc/base: access block device registers")

Cc: stable@dpdk.org

Signed-off-by: Abhishek Maheshwari <abhishek.maheshwari@intel.com>

---
v2:
* Fixing the styling issues
* Addressing comment to avoid reading the register again after
  exhausting the tries

v3:
* Fixing warning condition

v4:
* Fixing print argument format to %u in warning

v5:
* Addressing comments based on input that line length limit is 100
---
 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..60555a6786 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_try;
 
 	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_try = 10;
+		while (q_disable_try-- && IFCVF_READ_REG16(&cfg->queue_enable))
+			msec_delay(10);
+
+		if (!q_disable_try)
+			WARNINGOUT("Failed to disable Q:%u, Saved state could be invalid\n", 
+i);
+
 		if (hw->device_type == IFCVF_BLK)
 			ring_state = *(u32 *)(hw->lm_cfg +
 					IFCVF_LM_RING_STATE_OFFSET +
--
2.31.1
Ack. Reviewed by Purna Chandra Mandal <purna.chandra,mandal@intel.com>