[virtio-dev] [PATCH 09/11] transport-pci: Describe PCI MMR dev config registers

[Parav Pandit <parav@nvidia.com>]

Legacy virtio configuration registers and adjacent
device configuration registers are located somewhere
in a memory BAR.

A new capability supplies the location of these registers
which a driver can use to map I/O access to legacy
memory mapped registers.

This gives the ability to locate legacy registers in either
the existing memory BAR or as completely new BAR at BAR 0.

A below example diagram attempts to depicts it in an existing
memory BAR.

+------------------------------+
|Transitional                  |
|MMR SRIOV VF                  |
|                              |
++---------------+             |
||dev_id =       |             |
||{0x10f9-0x10ff}|             |
|+---------------+             |
|                              |
++--------------------+        |
|| PCIe ext cap = 0xB |        |
|| cfg_type = 10      |        |
|| offset   = 0x1000  |        |
|| bar      = A {0..5}|        |
|+--|-----------------+        |
|   |                          |
|   |                          |
|   |    +-------------------+ |
|   |    | Memory BAR = A    | |
|   |    |                   | |
|   +------>+--------------+ | |
|        |  |legacy virtio | | |
|        |  |+ dev cfg     | | |
|        |  |registers     | | |
|        |  +--------------+ | |
|        +-----------------+ | |
+------------------------------+

Co-developed-by: Satananda Burla <sburla@marvell.com>
Signed-off-by: Parav Pandit <parav@nvidia.com>
---
 transport-pci.tex | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/transport-pci.tex b/transport-pci.tex
index aeda4a1..55a6aa0 100644
--- a/transport-pci.tex
+++ b/transport-pci.tex
@@ -168,6 +168,7 @@ \subsection{Virtio Structure PCI Capabilities}\label{sec:Virtio Transport Option
 \item ISR Status
 \item Device-specific configuration (optional)
 \item PCI configuration access
+\item Legacy memory mapped configuration registers (optional)
 \end{itemize}
 
 Each structure can be mapped by a Base Address register (BAR) belonging to
@@ -228,6 +229,8 @@ \subsection{Virtio Structure PCI Capabilities}\label{sec:Virtio Transport Option
 #define VIRTIO_PCI_CAP_SHARED_MEMORY_CFG 8
 /* Vendor-specific data */
 #define VIRTIO_PCI_CAP_VENDOR_CFG        9
+/* Legacy configuration registers capability */
+#define VIRTIO_PCI_CAP_LEGACY_MMR_CFG    10
 \end{lstlisting}
 
         Any other value is reserved for future use.
@@ -682,6 +685,18 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
 Configuration Space / Legacy Interface: Device Configuration
 Space}~\nameref{sec:Basic Facilities of a Virtio Device / Device Configuration Space / Legacy Interface: Device Configuration Space} for workarounds.
 
+\paragraph{Transitional MMR Interface: A Note on Configuration Registers}
+\label{sec:Virtio Transport Options / Virtio Over PCI Bus / Virtio Structure PCI Capabilities / Common configuration structure layout / Transitional MMR Interface: A Note on Configuration Registers}
+
+The transitional MMR device MUST present legacy virtio registers
+consisting of legacy common configuration registers followed by
+legacy device specific configuration registers described in section
+\ref{sec:Virtio Transport Options / Virtio Over PCI Bus / Virtio Structure PCI Capabilities / Common configuration structure layout / Legacy Interfaces: A Note on Configuration Registers}
+in a memory region PCI BAR.
+
+The transitional MMR device MUST provide the location of the
+legacy virtio configuration registers using a legacy memory mapped
+registers capability described in section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / Virtio Structure PCI Capabilities / Transitional MMR Interface: Legacy Memory Mapped Configuration Registers Capability}.
 
 \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
 
@@ -956,9 +971,23 @@ \subsubsection{PCI configuration access capability}\label{sec:Virtio Transport O
 specified by some other Virtio Structure PCI Capability
 of type other than \field{VIRTIO_PCI_CAP_PCI_CFG}.
 
+\subsubsection{Transitional MMR Interface: Legacy Memory Mapped Configuration Registers Capability}
+\label{sec:Virtio Transport Options / Virtio Over PCI Bus / Virtio Structure PCI Capabilities / Transitional MMR Interface: Legacy Memory Mapped Configuration Registers Capability}
+
+The optional VIRTIO_PCI_CAP_LEGACY_MMR_CFG capability defines
+the location of the legacy virtio configuration registers
+followed by legacy device specific configuration registers in
+the memory region BAR for the transitional MMR device.
+
+The \field{cap.offset} MUST be 4-byte aligned.
+The \field{cap.offset} SHOULD be 4KBytes aligned and
+\field{cap.length} SHOULD be 4KBytes.
+
+The transitional MMR device MUST present a legacy configuration
+memory mapped registers capability using \field{virtio_pcie_ext_cap}.
+
 \subsubsection{Legacy Interface: A Note on Feature Bits}
-\label{sec:Virtio Transport Options / Virtio Over PCI Bus /
-Virtio Structure PCI Capabilities / Legacy Interface: A Note on Feature Bits}
+\label{sec:Virtio Transport Options / Virtio Over PCI Bus / Virtio Structure PCI Capabilities / Legacy Interface: A Note on Feature Bits}
 
 Only Feature Bits 0 to 31 are accessible through the
 Legacy Interface. When used through the Legacy Interface,
-- 
2.26.2


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