[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: [PATCH virtio] virtio-iommu: Add built-in topology description
Add a simple method to describe the IOMMU topology in the config space, guarded by a new feature bit. A list of capabilities in the config space describes the devices managed by the IOMMU and their endpoint IDs. As outlined in paragraph #1 below, the method used to describe I/O topology depends on the platform. Device-Tree based platforms use the "iommus" and "iommu-map" DT properties, while ACPI based platforms will use the VIOT table (whose format is compatible with this built-in description, but is under discussion). This adds a method for lightweight platforms that don't use either DT or ACPI. Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org> --- virtio-iommu.tex | 102 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 102 insertions(+) diff --git a/virtio-iommu.tex b/virtio-iommu.tex index 08b358a..a1de2a8 100644 --- a/virtio-iommu.tex +++ b/virtio-iommu.tex @@ -67,6 +67,9 @@ \subsection{Feature bits}\label{sec:Device Types / IOMMU Device / Feature bits} \item[VIRTIO_IOMMU_F_MMIO (5)] The VIRTIO_IOMMU_MAP_F_MMIO flag is available. + +\item[VIRTIO_IOMMU_F_TOPOLOGY (6)] + Topology description is available at \field{topo_config}. \end{description} \drivernormative{\subsubsection}{Feature bits}{Device Types / IOMMU Device / Feature bits} @@ -97,6 +100,10 @@ \subsection{Device configuration layout}\label{sec:Device Types / IOMMU Device / le32 end; } domain_range; le32 probe_size; + struct virtio_iommu_topo_config { + le16 num_items; + le16 offset; + } topo_config; }; \end{lstlisting} @@ -139,6 +146,101 @@ \subsection{Device initialization}\label{sec:Device Types / IOMMU Device / Devic If the driver does not accept the VIRTIO_IOMMU_F_BYPASS feature, the device SHOULD NOT let endpoints access the guest-physical address space. +\subsubsection{Built-in topology description}\label{sec:Device Types / IOMMU Device / Device initialization / topology} + +The device manages memory accesses from endpoints, identified by endpoint +IDs. The driver can discover which endpoint ID corresponds to an endpoint +using a method specific to the platform. Platforms described with device +tree use the \texttt{iommus} and \texttt{iommu-map} properties embedded +into device nodes for this purpose. Platforms described with ACPI use a +table such as the Virtual I/O Translation Table (VIOT). Platforms that do +not support either device tree or ACPI may embed a minimalistic +description in the device configuration space, declared by the +VIRTIO_IOMMU_F_TOPOLOGY feature. + +A disadvantage of describing the topology from within the device is the +lack of initialization ordering information. Out-of-band descriptions such +as device tree and ACPI let the operating system know about device +dependencies so that it can initialize supplier devices (IOMMUs) before +their consumers (endpoints). Platforms using the VIRTIO_IOMMU_F_TOPOLOGY +feature have to communicate the device dependency in another way. + +If the VIRTIO_IOMMU_F_TOPOLOGY feature is negotiated, \field{topo_config} +describes the topology description array. \field{topo_config.offset} is +the offset between the beginning of the device-specific configuration +space (struct virtio_iommu_config) and the array. The array is composed of +\field{topo_config.num_items} topology structures. A topology structure +defines the endpoint ID of one or more endpoints managed by the +virtio-iommu device. Each structure has a \field{length} field, which +defines the offset to the next structure. Each structure starts with a +\field{type} byte: + +\begin{description} + \item[VIRTIO_IOMMU_TOPO_PCI_RANGE (1)] struct virtio_iommu_topo_pci_range + \item[VIRTIO_IOMMU_TOPO_MMIO (2)] struct virtio_iommu_topo_mmio +\end{description} + +To stay binary compatible with ACPI VIOT, types 3 and 4 are currently +reserved. + +\paragraph{PCI range}\label{sec:Device Types / IOMMU Device / Device initialization / topology / PCI range} + +\begin{lstlisting} +struct virtio_iommu_topo_pci_range { + u8 type; + u8 reserved; + le16 length; + le32 endpoint_start; + le16 segment; + le16 bdf_start; + le16 bdf_end; + le16 padding; +}; +\end{lstlisting} + +The PCI range structure describes the endpoint IDs of a series of PCI +devices identified by their BDF (Bus-Device-Function) number. + +\begin{description} + \item[\field{type}] VIRTIO_IOMMU_TOPO_PCI_RANGE. + \item[\field{length}] Length of the structure in bytes. + \item[\field{endpoint_start}] First endpoint ID. + \item[\field{segment}] Identifier of the PCI hierarchy. Sometimes called + domain number. + \item[\field{bdf_start}] First BDF in the range. + \item[\field{bdf_end}] Last BDF in the range. +\end{description} + +The correspondence between a PCI BDF in the range +[ bdf_start; bdf_end ] and its endpoint IDs is a linear transformation: +endpoint_id = bdf - bdf_start + endpoint_start. + +\paragraph{Single endpoint}\label{sec:Device Types / IOMMU Device / Device initialization / topology / Single endpoint} + +\begin{lstlisting} +struct virtio_iommu_topo_mmio { + u8 type; + u8 reserved; + le16 length; + le32 endpoint; + le64 address; +}; +\end{lstlisting} + +This structure describes a single endpoint. + +\begin{description} + \item[\field{type}] VIRTIO_IOMMU_TOPO_MMIO. + \item[\field{length}] Length of the structure in bytes. + \item[\field{endpoint}] The endpoint ID. + \item[\field{address}] The first MMIO address in the physical address + space. +\end{description} + +\devicenormative{\paragraph}{Built-in topology description}{Device Types / IOMMU Device / Device initialization / topology} + +\field{topo_config.offset} SHOULD be aligned on 8 bytes. + \subsection{Device operations}\label{sec:Device Types / IOMMU Device / Device operations} Driver send requests on the request virtqueue, notifies the device and -- 2.27.0
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]