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| -rw-r--r-- | content.tex | 37 |
1 files changed, 18 insertions, 19 deletions
diff --git a/content.tex b/content.tex index 9120730..5a1a989 100644 --- a/content.tex +++ b/content.tex @@ -1636,10 +1636,25 @@ 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} +All known legacy drivers check either the PCI Revision or the +Device and Vendor IDs, and thus won't attempt to drive a +non-transitional device. + +A buggy legacy driver might mistakenly attempt to drive a +non-transitional device. If support for such drivers is required +(as opposed to fixing the bug), the following would be the +recommended way to detect and handle them. +\begin{note} +Such buggy drivers are not currently known to be used in +production. +\end{note} + +\devicenormative{\paragraph}{Non-transitional Device With Legacy Driver}{Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Non-transitional Device With Legacy Driver} 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: +a legacy device with the same ID (including PCI Revision, Device +and Vendor IDs) is known to have previously existed, +SHOULD take the following steps to cause the legacy driver to +fail gracefully when it attempts to drive them: \begin{enumerate} \item Present an I/O BAR in BAR0, and @@ -1660,22 +1675,6 @@ As a prerequisite to device initialization, the driver scans the PCI capability list, detecting virtio configuration layout using Virtio Structure PCI capabilities as detailed in \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / Virtio Structure PCI Capabilities} -\paragraph{Non-transitional Device With Legacy Driver}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Non-transitional Device With Legacy Driver} - -\devicenormative{\subparagraph}{Non-transitional Device With Legacy Driver}{Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Non-transitional Device With Legacy Driver} - -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: - -\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} - \subparagraph{Legacy Interface: A Note on Device Layout Detection}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtio Device Configuration Layout Detection / Legacy Interface: A Note on Device Layout Detection} Legacy drivers skipped the Device Layout Detection step, assuming legacy |