[PATCH] vdpa/sfc: handle sync issue between qemu and vhost-user

[<abhimanyu.saini@xilinx.com>]

From: Abhimanyu Saini <absaini@amd.com>

When DPDK app is running in the VF, it sometimes rings the doorbell
before dev_config has had a chance to complete and hence it misses
the event. As workaround, ring the doorbell when vDPA reports the
notify_area to QEMU.

Fixes: 5e7596ba7cb3 ("vdpa/sfc: introduce Xilinx vDPA driver")
Cc: stable@dpdk.org

Signed-off-by: Vijay Kumar Srivastava <vsrivast@xilinx.com>
Signed-off-by: Abhimanyu Saini <absaini@amd.com>
---
 drivers/vdpa/sfc/sfc_vdpa_ops.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/vdpa/sfc/sfc_vdpa_ops.c b/drivers/vdpa/sfc/sfc_vdpa_ops.c
index b3d9b6c..63aa52d 100644
--- a/drivers/vdpa/sfc/sfc_vdpa_ops.c
+++ b/drivers/vdpa/sfc/sfc_vdpa_ops.c
@@ -794,6 +794,8 @@
 	int vfio_dev_fd;
 	efx_rc_t rc;
 	unsigned int bar_offset;
+	volatile void *doorbell;
+	struct rte_pci_device *pci_dev;
 	struct rte_vdpa_device *vdpa_dev;
 	struct sfc_vdpa_ops_data *ops_data;
 	struct vfio_region_info reg = { .argsz = sizeof(reg) };
@@ -856,6 +858,18 @@
 	sfc_vdpa_info(dev, "vDPA ops get_notify_area :: offset : 0x%" PRIx64,
 		      *offset);
 
+	pci_dev = sfc_vdpa_adapter_by_dev_handle(dev)->pdev;
+	doorbell = (uint8_t *)pci_dev->mem_resource[reg.index].addr + *offset;
+
+	/*
+	 * virtio-net driver in VM sends queue notifications before
+	 * vDPA has a chance to setup the queues and notification area,
+	 * and hence the HW misses these doorbell notifications.
+	 * Since, it is safe to send duplicate doorbell, send another
+	 * doorbell from vDPA driver as workaround for this timing issue.
+	 */
+	rte_write16(qid, doorbell);
+
 	return 0;
 }
 
-- 
1.8.3.1