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| -rw-r--r-- | content.tex | 27 |
1 files changed, 24 insertions, 3 deletions
diff --git a/content.tex b/content.tex index c91dd69..cb0d648 100644 --- a/content.tex +++ b/content.tex @@ -962,7 +962,10 @@ The Subsystem Vendor ID SHOULD reflect the PCI Vendor ID of the environment (it's currently only used for informational purposes by the driver). -Non-transitional devices MUST have a Revision ID of 1 or higher. +Non-transitional devices SHOULD have a Revision ID of 1 or higher. + +This is to reduce the chance of a legacy driver attempting +to drive the device. \drivernormative{\subsubsection}{PCI Device Discovery}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Discovery} All drivers MUST match devices with any Revision ID, this @@ -971,8 +974,9 @@ is to allow devices to be versioned without breaking drivers. Drivers MUST match any Revision ID value. \subsubsection{Legacy Interfaces: A Note on PCI Device Discovery}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Discovery / Legacy Interfaces: A Note on PCI Device Discovery} -Transitional devices MUST have a Revision ID of 0 to match -legacy drivers. +Transitional devices MUST have a Revision ID of 0. + +This is to match legacy drivers. \subsection{PCI Device Layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout} @@ -1508,6 +1512,23 @@ see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space / Legacy Interface: Device Configuration Space}~\nameref{sec:Basic Facilities of a Virtio Device / Device Configuration Space / Legacy Interface: Device Configuration Space} for workarounds. +\subsubsection{Non-transitional Device With Legacy Driver: A Note +on PCI Device Layout}\label{sec:Virtio Transport Options / Virtio +Over PCI Bus / PCI Device Layout / Non-transitional Device With +Legacy Driver: A Note on PCI Device Layout} + +Non-transitional devices, on a platform where a legacy driver for +a legacy device with the same ID might have previously existed, +SHOULD take the following steps to fail gracefully when a legacy +driver attempts to drive them: + +\begin{enumerate} +\item Present an I/O BAR in BAR0, and +\item 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. +\end{enumerate} + \subsection{PCI-specific Initialization And Device Operation}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation} \subsubsection{Device Initialization}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization} |