[PATCH] virtio-mmio: add support for transport version 3

[Peter Hilber <peter.hilber@oss.qualcomm.com>]

Virtio MMIO transport version 3 allows device reset to complete
asynchronously. Unlike version 2, where writing zero to Status must
complete the reset before the write returns, version 3 requires the
driver to poll Status until it reads back zero before considering reset
complete.

Update virtio-mmio accordingly: accept transport version 3 and, during
reset, wait for Status to become zero. Keep the polling loop unbounded,
consistent with virtio-pci, since the reset callback does not return an
error code.

Signed-off-by: Peter Hilber <peter.hilber@oss.qualcomm.com>
Link: https://github.com/oasis-tcs/virtio-spec/commit/bb1dd2e1fe89b862f38f15873d835a698b196f89
---
 drivers/virtio/virtio_mmio.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 510b7c4efdff..316f03b97356 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -55,6 +55,7 @@
 #define pr_fmt(fmt) "virtio-mmio: " fmt
 
 #include <linux/acpi.h>
+#include <linux/delay.h>
 #include <linux/dma-mapping.h>
 #include <linux/highmem.h>
 #include <linux/interrupt.h>
@@ -114,9 +115,9 @@ static int vm_finalize_features(struct virtio_device *vdev)
 	vring_transport_features(vdev);
 
 	/* Make sure there are no mixed devices */
-	if (vm_dev->version == 2 &&
+	if (vm_dev->version >= 2 &&
 			!__virtio_test_bit(vdev, VIRTIO_F_VERSION_1)) {
-		dev_err(&vdev->dev, "New virtio-mmio devices (version 2) must provide VIRTIO_F_VERSION_1 feature!\n");
+		dev_err(&vdev->dev, "New virtio-mmio devices (version >= 2) must provide VIRTIO_F_VERSION_1 feature!\n");
 		return -EINVAL;
 	}
 
@@ -254,6 +255,12 @@ static void vm_reset(struct virtio_device *vdev)
 
 	/* 0 status means a reset. */
 	writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
+
+	if (vm_dev->version >= 3) {
+		/* Wait for reset to complete. */
+		while (vm_get_status(vdev))
+			fsleep(1000);
+	}
 }
 
 
@@ -600,7 +607,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 
 	/* Check device version */
 	vm_dev->version = readl(vm_dev->base + VIRTIO_MMIO_VERSION);
-	if (vm_dev->version < 1 || vm_dev->version > 2) {
+	if (vm_dev->version < 1 || vm_dev->version > 3) {
 		dev_err(&pdev->dev, "Version %ld not supported!\n",
 				vm_dev->version);
 		rc = -ENXIO;
-- 
2.43.0