FAILED: patch "[PATCH] virtio/s390: implement virtio-ccw revision 2 correctly" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 182f709c5cff683e6732d04c78e328de0532284f Mon Sep 17 00:00:00 2001
From: Cornelia Huck <[email protected]>
Date: Tue, 16 Feb 2021 12:06:45 +0100
Subject: [PATCH] virtio/s390: implement virtio-ccw revision 2 correctly

CCW_CMD_READ_STATUS was introduced with revision 2 of virtio-ccw, and drivers should only rely on it being implemented when they negotiated at least that revision with the device.

However, virtio_ccw_get_status() issued READ_STATUS for any device operating at least at revision 1. If the device accepts READ_STATUS regardless of the negotiated revision (which some implementations like QEMU do, even though the spec currently does not allow it), everything works as intended. While a device rejecting the command should also be handled gracefully, we will not be able to see any changes the device makes to the status, such as setting NEEDS_RESET or setting the status to zero after a completed reset.

We negotiated the revision to at most 1, as we never bumped the maximum revision; let's do that now and properly send READ_STATUS only if we are operating at least at revision 2.

index 5730572b52cd..54e686dca6de 100644
@@ -117,7 +117,7 @@ struct virtio_rev_info {
 };
 
 /* the highest virtio-ccw revision we support */
-#define VIRTIO_CCW_REV_MAX 1
+#define VIRTIO_CCW_REV_MAX 2
 
 struct virtio_ccw_vq_info {
 	struct virtqueue *vq;

@@ -952,7 +952,7 @@ static u8 virtio_ccw_get_status(struct virtio_device *vdev)
 	u8 old_status = vcdev->dma_area->status;
 	struct ccw1 *ccw;
 
-	if (vcdev->revision < 1)
+	if (vcdev->revision < 2)
 		return vcdev->dma_area->status;
 
 	ccw = ccw_device_dma_zalloc(vcdev->cdev, sizeof(*ccw));