[PATCH] pci: a note on non-transitional devices

Add a note documenting handling legacy drivers for non transitional devices.  VIRTIO-34  Signed-off-by: Michael S. Tsirkin <> ---  virtio-v1.0-wd01-part1-specification.txt
17 ++++++++++++++++-  1 file changed, 16 insertions(+), 1 deletion(-)  diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt index 8a649f2..6ab4ff8 100644 --- a/virtio-v1.0-wd01-part1-specification.txt +++ b/virtio-v1.0-wd01-part1-specification.txt @@ -1171,7 +1171,22 @@ space in BAR0.
Transitional drivers should look for the Virtio PCI  Capabilities on the capability list. -If there are not present, driver should assume a legacy device. +If these are not present, driver should assume a legacy device. + +Non-transitional drivers should look for the Virtio PCI +Capabilities on the capability list. +If these are not present, driver should assume a legacy device, +and fail gracefully. + +Non-transitional devices, on a platform where a legacy driver for +a legacy device with the same ID might have previously existed, +must take the following steps to fail gracefully when a legacy +driver attempts to drive them: + +1) Present an I/O BAR in BAR0, and +2) Respond to a single-byte zero write to offset 18 +
(corresponding to Device Status register in the legacy layout) +
of BAR0 by presenting zeroes on every BAR and ignoring writes.
2.3.1.3.1.1. Queue Vector Configuration

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