[PATCH 1/4] virtio-mmio: wait for status readback after reset

[Andrew Stellman <astellman@stellman-greene.com>]

The virtio specification requires that after writing 0 to the status
register, the driver must wait until the device has actually completed
the reset (status reads back as 0) before proceeding. vm_reset() writes
0 but returns immediately without confirming the device has reset.

Add a poll loop matching the pattern already used in virtio-pci's
vp_reset(), which calls msleep(1) in a loop until the status register
reads 0.

Signed-off-by: Andrew Stellman <astellman@stellman-greene.com>
---
 drivers/virtio/virtio_mmio.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 595c227..a477977 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -56,6 +56,7 @@
 
 #include <linux/acpi.h>
 #include <linux/dma-mapping.h>
+#include <linux/delay.h>
 #include <linux/highmem.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
@@ -254,6 +255,8 @@ static void vm_reset(struct virtio_device *vdev)
 
 	/* 0 status means a reset. */
 	writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
+	while (readl(vm_dev->base + VIRTIO_MMIO_STATUS))
+		msleep(1);
 }
 
 
-- 
2.34.1