diff options
| -rw-r--r-- | content.tex | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/content.tex b/content.tex index 6433226..fafa532 100644 --- a/content.tex +++ b/content.tex @@ -651,7 +651,8 @@ struct virtio_pci_cap { u8 cap_len; /* Generic PCI field: capability length */ u8 cfg_type; /* Identifies the structure. */ u8 bar; /* Where to find it. */ - u8 padding[3]; /* Pad to full dword. */ + u8 id; /* Multiple capabilities of the same type */ + u8 padding[2]; /* Pad to full dword. */ le32 offset; /* Offset within bar. */ le32 length; /* Length of the structure, in bytes. */ }; @@ -697,7 +698,8 @@ The fields are interpreted as follows: The device MAY offer more than one structure of any type - this makes it possible for the device to expose multiple interfaces to drivers. The order of the capabilities in the capability list specifies the order of preference - suggested by the device. + suggested by the device. A device may specify that this ordering mechanism be + overridden by the use of the \field{id} field. \begin{note} For example, on some hypervisors, notifications using IO accesses are faster than memory accesses. In this case, the device would expose two @@ -716,6 +718,12 @@ The fields are interpreted as follows: Any other value is reserved for future use. +\item[\field{id}] + Used by some device types to uniquely identify multiple capabilities + of a certain type. If the device type does not specify the meaning of + this field, its contents are undefined. + + \item[\field{offset}] indicates where the structure begins relative to the base address associated with the BAR. The alignment requirements of \field{offset} are indicated |