[virtio-comment] [PATCH v4 3/3] shared memory: Define mmio registers

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

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

Define an MMIO interface to discover and map shared
memory regions.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 content.tex | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/content.tex b/content.tex
index ddbf949..f2195be 100644
--- a/content.tex
+++ b/content.tex
@@ -1726,6 +1726,33 @@ All register values are organized as Little Endian.
     selected by writing to \field{QueueSel}.
   }
   \hline 
+  \mmioreg{SHMSel}{Shared memory id}{0x0ac}{W}{%
+    Writing to this register selects the shared memory region \ref{sec:Basic Facilities of a Virtio Device / Shared Memory Regions}
+    following operations on \field{SHMLenLow}, \field{SHMLenHigh},
+    \field{SHMBaseLow} and \field{SHMBaseHigh} apply to.
+  }
+  \hline 
+  \mmiodreg{SHMLenLow}{SHMLenHigh}{Shared memory region 64 bit long length}{0x0b0}{0x0xb4}{R}{%
+    These registers return the length of the shared memory
+    region in bytes, as defined by the device for the region selected by
+    the \field{SHMSel} register.  The lower 32 bits of the length
+    are read from \field{SHMLenLow} and the higher 32 bits from
+    \field{SHMLenHigh}.  Reading from a non-existent
+    region (i.e. where the ID written to \field{SHMSel} is unused)
+    results in a length of -1.
+  }
+  \hline 
+  \mmiodreg{SHMBaseLow}{SHMBaseHigh}{Shared memory region 64 bit long physical address}{0x0b8}{0x0xbc}{R}{%
+    The driver reads these registers to discover the base address
+    of the region in physical address space.  This address is
+    chosen by the device (or other part of the VMM).
+    The lower 32 bits of the address are read from \field{SHMBaseLow}
+    with the higher 32 bits from \field{SHMBaseHigh}.  Reading
+    from a non-existent region (i.e. where the ID written to
+    \field{SHMSel} is unused) results in a base address of
+    0xffffffffffffffff.
+  }
+  \hline 
   \mmioreg{ConfigGeneration}{Configuration atomicity value}{0x0fc}{R}{
     Reading from this register returns a value describing a version of the device-specific configuration space (see \field{Config}).
     The driver can then access the configuration space and, when finished, read \field{ConfigGeneration} again.
@@ -1815,6 +1842,9 @@ If both values are valid, it MUST read \field{DeviceID}
 and if its value is zero (0x0) MUST abort initialization and
 MUST NOT access any other register.
 
+Drivers not expecting shared memory MUST NOT use the shared
+memory registers.
+
 Further initialization MUST follow the procedure described in
 \ref{sec:General Initialization And Device Operation / Device Initialization}~\nameref{sec:General Initialization And Device Operation / Device Initialization}.
 
-- 
2.20.1


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