[PATCH 2/3] shared memory: Define PCI capability

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Define the PCI capability used for enumerating shared memory regions.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 content.tex | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/content.tex b/content.tex
index 321a2f4..776162a 100644
--- a/content.tex
+++ b/content.tex
@@ -649,6 +649,8 @@ The fields are interpreted as follows:
 #define VIRTIO_PCI_CAP_DEVICE_CFG        4
 /* PCI configuration access */
 #define VIRTIO_PCI_CAP_PCI_CFG           5
+/* Shared memory region */
+#define VIRTIO_PCI_CAP_SHARED_MEMORY_CFG 8
 \end{lstlisting}
 
         Any other value is reserved for future use.
@@ -987,6 +989,41 @@ any device type which has a device-specific configuration.
 
 The \field{offset} for the device-specific configuration MUST be 4-byte aligned.
 
+\subsubsection{Shared memory capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Shared memory capability}
+
+Shared memory regions \ref{sec:Basic Facilities of a Virtio
+Device / Shared Memory Regions} are enumerated on the PCI transport
+as a sequence of VIRTIO_PCI_CAP_SHARED_MEMORY_CFG capabilities, one per region.
+
+The capability is immediately followed by an additional field like so:
+
+\begin{lstlisting}
+struct virtio_pci_shm_cap {
+        struct virtio_pci_cap cap;
+        u32 offset_hi;
+        u32 length_hi;
+        u8  id;
+};
+\end{lstlisting}
+
+Given that the \field{cap.length} and \field{cap.offset} fields
+are only 32 bit, the additional \field{offset_hi} and \field {length_hi}
+fields provide the most significant 32 bits of a total 64 bit offset and
+length within the bar specified by \field{cap.bar}.  \field{id}
+uniquely identifies the given shared memory region using a device
+specific identifier.
+
+While most capabilities can not be repeated, multiple
+VIRTIO_PCI_CAP_SHARED_MEMORY_CFG capabilities are allowed as long
+as the \field{id} is unique.
+
+\devicenormative{\paragraph}{Device-specific configuration}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Shared memory capability}
+
+The region defined by the combination of the offsets and length
+fields MUST be contained within the declared bar.
+
+The \field{id} MUST be unique for any one device instance.
+
 \subsubsection{PCI configuration access capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / PCI configuration access capability}
 
 The VIRTIO_PCI_CAP_PCI_CFG capability
-- 
2.20.1