[PATCH] pci: strengthen requirement of the correct subsystem id

If a hardware implementation of virtio does not have
the correct subsystem id, then drivers can't report
ir properly, or detect and work around bugs.
Change the requirement from MAY to SHOULD.

We can't make it a MUST since we did not require this
historically.

Signed-off-by: Michael S. Tsirkin <>
---
 content.tex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/content.tex b/content.tex
index 4bcb728..8f1518c 100644
--- a/content.tex
+++ b/content.tex
@@ -562,7 +562,7 @@ \subsection{PCI Device Discovery}\label{sec:Virtio Transport Options / Virtio Ov
 For example, the network card device with the Virtio Device ID 1
 has the PCI Device ID 0x1041 or the Transitional PCI Device ID 0x1000.
 
-The PCI Subsystem Vendor ID and the PCI Subsystem Device ID MAY reflect
+The PCI Subsystem Vendor ID and the PCI Subsystem Device ID SHOULD reflect
 the PCI Vendor and Device ID of the environment (for informational purposes by the driver).
 
 Non-transitional devices SHOULD have a PCI Device ID in the range
-- 
MST