[PATCH v2] vp_vdpa: harden the logic of set status

["Longpeng(Mike)" <longpeng2@huawei.com>]

From: Longpeng <longpeng2@huawei.com>

1. We should not set status to 0 when invoking vp_vdpa_set_status(),
   trigger a warning in that case.

2. The driver MUST wait for a read of device_status to return 0 before
   reinitializing the device. But we also don't want to keep us in an
   infinite loop forever, so wait for 5s if we try to reset the device.

Signed-off-by: Longpeng <longpeng2@huawei.com>
---
Changes v1->v2:
  - use WARN_ON instead of BUG_ON. [Stefano]
  - use "warning + failed" instead of "infinite loop". [Jason, Stefano]
  - use usleep_range instead of msleep (checkpatch). [Longpeng]

---
 drivers/vdpa/virtio_pci/vp_vdpa.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
index 13701c2a1963..a2d3b13ac646 100644
--- a/drivers/vdpa/virtio_pci/vp_vdpa.c
+++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
@@ -214,6 +214,9 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
 	struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
 	u8 s = vp_vdpa_get_status(vdpa);
 
+	/* We should never be setting status to 0. */
+	WARN_ON(status == 0);
+
 	if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
 	    !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
 		vp_vdpa_request_irq(vp_vdpa);
@@ -222,14 +225,33 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
 	vp_modern_set_status(mdev, status);
 }
 
+#define VP_VDPA_RESET_TMOUT_MS 5000 /* 5s */
+
 static int vp_vdpa_reset(struct vdpa_device *vdpa, bool clear)
 {
 	struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
 	struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
 	u8 s = vp_vdpa_get_status(vdpa);
+	unsigned long timeout;
 
 	vp_modern_set_status(mdev, 0);
 
+	/*
+	 * As the virtio v1.1 spec (4.1.4.3.2) says: After writing 0 to
+	 * device_status, the driver MUST wait for a read of device_status
+	 * to return 0 before reinitializing the device.
+	 * To avoid keep us here forever, we only wait for 5 seconds.
+	 */
+	timeout = jiffies + msecs_to_jiffies(VP_VDPA_RESET_TMOUT_MS);
+	while (vp_modern_get_status(mdev)) {
+		usleep_range(1000, 1500);
+		if (time_after(jiffies, timeout)) {
+			dev_err(&mdev->pci_dev->dev,
+				"vp_vdpa: fail to reset device\n");
+			return -ETIMEDOUT;
+		}
+	}
+
 	if (s & VIRTIO_CONFIG_S_DRIVER_OK)
 		vp_vdpa_free_irq(vp_vdpa);
 
-- 
2.23.0