[PATCH v3] 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 v3->v2:
 - move VP_VDPA_RESET_TIMEOUT_US near the other macros. [Stefano]
 - refer v1.2 in comments. [Stefano]
 - s/keep/keeping/  [Jason]
 - use readx_poll_timeout. [Jason]

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, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
index d448db0c4de3..3fc496aea456 100644
--- a/drivers/vdpa/virtio_pci/vp_vdpa.c
+++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
@@ -10,6 +10,7 @@
 
 #include <linux/interrupt.h>
 #include <linux/module.h>
+#include <linux/iopoll.h>
 #include <linux/pci.h>
 #include <linux/vdpa.h>
 #include <linux/virtio.h>
@@ -22,6 +23,7 @@
 #define VP_VDPA_QUEUE_MAX 256
 #define VP_VDPA_DRIVER_NAME "vp_vdpa"
 #define VP_VDPA_NAME_SIZE 256
+#define VP_VDPA_RESET_TIMEOUT_US 5000000 /* 5s */
 
 struct vp_vring {
 	void __iomem *notify;
@@ -214,6 +216,9 @@ 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);
@@ -226,10 +231,25 @@ static int vp_vdpa_reset(struct vdpa_device *vdpa)
 {
 	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);
+	u8 tmp, s = vp_vdpa_get_status(vdpa);
+	int ret;
 
 	vp_modern_set_status(mdev, 0);
 
+	/*
+	 * As the virtio v1.1/v1.2 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 keeping us here forever, we only wait for 5 seconds.
+	 */
+	ret = readx_poll_timeout(vp_ioread8, &mdev->common->device_status, tmp,
+				 tmp == 0, 1000, VP_VDPA_RESET_TIMEOUT_US);
+	if (ret) {
+		dev_err(&mdev->pci_dev->dev,
+			"vp_vdpa: fail to reset device, %d\n", ret);
+		return ret;
+	}
+
 	if (s & VIRTIO_CONFIG_S_DRIVER_OK)
 		vp_vdpa_free_irq(vp_vdpa);
 
-- 
2.23.0