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Diffstat (limited to 'content.tex')
| -rw-r--r-- | content.tex | 109 |
1 files changed, 6 insertions, 103 deletions
diff --git a/content.tex b/content.tex index ae5fa4c..7a92cb1 100644 --- a/content.tex +++ b/content.tex @@ -283,49 +283,9 @@ Packed Virtqueues}). Every driver and device supports either the Packed or the Split Virtqueue format, or both. -\subsection{Driver notifications} \label{sec:Virtqueues / Driver notifications} -The driver is sometimes required to notify the device after -making changes to the virtqueue. - -When VIRTIO_F_NOTIFICATION_DATA has not been negotiated, -this notification involves sending the -virtqueue number to the device (method depending on the transport). - -However, some devices benefit from the ability to find out the number of -available descriptors in the ring without accessing the virtqueue in memory: -for efficiency or as a debugging aid. - -To help with these optimizations, when VIRTIO_F_NOTIFICATION_DATA -has been negotiated, driver notifications to the device include -the following information: - -\begin{description} -\item [VQ number] -\item [Offset] - Within the ring where the next available ring entry - will be written. - Without VIRTIO_F_RING_PACKED this refers to the - 15 least significant bits of the available index. - With VIRTIO_F_RING_PACKED this refers to the offset - (in units of descriptor entries) - within the descriptor ring where the next available - descriptor will be written. -\item [Wrap Counter] - With VIRTIO_F_RING_PACKED this is the wrap counter - referring to the next available descriptor. - Without VIRTIO_F_RING_PACKED this is the most significant bit - of the available index. -\end{description} - -Note that the driver can trigger multiple notifications even without -making any more changes to the ring. When VIRTIO_F_NOTIFICATION_DATA -has been negotiated, these notifications would then have -identical \field{Offset} and \field{Wrap Counter} values. - \input{split-ring.tex} \input{packed-ring.tex} - \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation} We start with an overview of device initialization, then expand on the @@ -902,9 +862,7 @@ the same Queue Notify address for all queues. \devicenormative{\paragraph}{Notification capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability} The device MUST present at least one notification capability. -For devices not offering VIRTIO_F_NOTIFICATION_DATA: - -The \field{cap.offset} MUST be 2-byte aligned. +The \field{cap.offset} MUST be 2-byte aligned. The device MUST either present \field{notify_off_multiplier} as an even power of 2, or present \field{notify_off_multiplier} as 0. @@ -918,23 +876,6 @@ For all queues, the value \field{cap.length} presented by the device MUST satisf cap.length >= queue_notify_off * notify_off_multiplier + 2 \end{lstlisting} -For devices offering VIRTIO_F_NOTIFICATION_DATA: - -The device MUST either present \field{notify_off_multiplier} as a -number that is a power of 2 that is also a multiple 4, -or present \field{notify_off_multiplier} as 0. - -The \field{cap.offset} MUST be 4-byte aligned. - -The value \field{cap.length} presented by the device MUST be at least 4 -and MUST be large enough to support queue notification offsets -for all supported queues in all possible configurations. - -For all queues, the value \field{cap.length} presented by the device MUST satisfy: -\begin{lstlisting} -cap.length >= queue_notify_off * notify_off_multiplier + 4 -\end{lstlisting} - \subsubsection{ISR status capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability} The VIRTIO_PCI_CAP_ISR_CFG capability @@ -1327,21 +1268,8 @@ separate cache lines. \subsubsection{Notifying The Device}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Notifying The Device} -When VIRTIO_F_NOTIFICATION_DATA has not been negotiated, -the driver notifies the device by writing the 16-bit virtqueue index -of this virtqueue (in little-endian byte order format) -to the Queue Notify address. - -When VIRTIO_F_NOTIFICATION_DATA has been negotiated, -the driver notifies the device by writing the following -32-bit value to the Queue Notify address: -\lstinputlisting{notifications-le.c} - -See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications} -for the definition of the components. - -See \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability} for how to calculate the -Queue Notify address. +The driver notifies the device by writing the 16-bit virtqueue index +of this virtqueue to the Queue Notify address. See \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability} for how to calculate this address. \subsubsection{Virtqueue Interrupts From The Device}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Virtqueue Interrupts From The Device} @@ -1572,19 +1500,8 @@ All register values are organized as Little Endian. } \hline \mmioreg{QueueNotify}{Queue notifier}{0x050}{W}{% - Writing a value this register notifies the device that - there are new buffers to process in a queue. - - When VIRTIO_F_NOTIFICATION_DATA has not been negotiated, - the value written is the queue index. - - When VIRTIO_F_NOTIFICATION_DATA has been negotiated, - the value has the following format: - - \lstinputlisting{notifications-le.c} - - See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications} - for the definition of the components. + Writing a queue index to this register notifies the device that + there are new buffers to process in the queue. } \hline \mmioreg{InterruptStatus}{Interrupt status}{0x60}{R}{% @@ -2423,22 +2340,12 @@ GPR & Input Value & Output Value \\ \hline 2 & Subchannel ID & Host Cookie \\ \hline - 3 & Notification data & \\ + 3 & Virtqueue number & \\ \hline 4 & Host Cookie & \\ \hline \end{tabular} -When VIRTIO_F_NOTIFICATION_DATA has not been negotiated, -the \field{Notification data} contains the Virtqueue number. - -When VIRTIO_F_NOTIFICATION_DATA has been negotiated, -the value has the following format: -\lstinputlisting{notifications-be.c} - -See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications} -for the definition of the components. - \devicenormative{\paragraph}{Guest->Host Notification}{Virtio Transport Options / Virtio over channel I/O / Device Operation / Guest->Host Notification} The device MUST ignore bits 0-31 (counting from the left) of GPR2. This aligns passing the subchannel ID with the way it is passed @@ -5441,10 +5348,6 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp \item[VIRTIO_F_IN_ORDER(35)] This feature indicates that all buffers are used by the device in the same order in which they have been made available. - \item[VIRTIO_F_NOTIFICATION_DATA(36)] This feature indicates - that drivers pass extra data (besides identifying the Virtqueue) - in their device notifications. - See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications}. \end{description} \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits} |