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Subject: Re: [PATCH virtio 1/1] Add "Group Identifier" support to virtio PCI capabilities.
On Tue, Jun 19, 2018 at 11:32:28AM -0500, Venu Busireddy wrote: > Add VIRTIO_PCI_CAP_GROUP_ID_CFG (Group Identifier) capability to the > virtio PCI capabilities to allow for the grouping of devices. > > Signed-off-by: Venu Busireddy <venu.busireddy@oracle.com> > --- > content.tex | 43 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 43 insertions(+) > > diff --git a/content.tex b/content.tex > index 7a92cb1..7ea6267 100644 > --- a/content.tex > +++ b/content.tex > @@ -599,6 +599,8 @@ The fields are interpreted as follows: > #define VIRTIO_PCI_CAP_DEVICE_CFG 4 > /* PCI configuration access */ > #define VIRTIO_PCI_CAP_PCI_CFG 5 > +/* Group Identifier */ > +#define VIRTIO_PCI_CAP_GROUP_ID_CFG 6 > \end{lstlisting} > > Any other value is reserved for future use. > @@ -997,6 +999,47 @@ address \field{cap.length} bytes within a BAR range > specified by some other Virtio Structure PCI Capability > of type other than \field{VIRTIO_PCI_CAP_PCI_CFG}. > > +\subsubsection{Group Identifier capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Group Identifier capability} > + > +The VIRTIO_PCI_CAP_GROUP_ID_CFG capability provides means for grouping devices together. > + > +The capability is immediately followed by an identifier of arbitrary size as below: > + > +\begin{lstlisting} > +struct virtio_pci_group_id_cap { > + struct virtio_pci_cap cap; > + u8 group_id[]; /* Group Identifier */ > +}; > +\end{lstlisting} > + > +The fields \field{cap.bar}, \field{cap.length}, \field{cap.offset} > +and \field{group_id} are read-only for the driver. > + > +The specification does not impose any restrictions on the size or > +structure of group_id[]. I think it must be a multiple of 4 in size, as is standard for all capabilities. > Vendors are free to declare this array as > +large as needed, as long as the combined size of all capabilities can > +be accommodated within the PCI configuration space. > + > +If there is enough room in the PCI configuration space to accommodate > +the group identifier, the fields \field{cap.bar}, \field{cap.offset} > +and \field{cap.length} should be set to 0. > + > +If there isn't enough room, some or all of the group identifier can be > +presented in the BAR region, in which case the fields \field{cap.bar}, > +\field{cap.offset} and \field{cap.length} should be set appropriately. And then how do you glue the two pieces? > + > +In either case, the field \field{cap.cap_len} indicates the length of > +the group identifier information present in the configuration space > +itself. It seems like an overkill to me. Isn't it enough to have it in config space? This would make comparisons easier. > + > +\devicenormative{\paragraph}{Group Identifier capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Group Identifier capability} > + > +The device MAY present the VIRTIO_PCI_CAP_GROUP_ID_CFG capability. > + > +\drivernormative{\paragraph}{Group Identifier capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Group Identifier capability} > + > +The driver MUST NOT write to group_id[] area or the BAR region. > + > \subsubsection{Legacy Interfaces: A Note on PCI Device Layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: A Note on PCI Device Layout} > > Transitional devices MUST present part of configuration
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