[PATCH v2 3/3] transport-mmio: introduce SHMPageShift register

[Sergio Lopez <slp@redhat.com>]

Introduce the "SHMPageShift" register which, when read, returns the
page shift value that can be used to derive the page size value
supported by the shared memory regions in the device.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 transport-mmio.tex | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/transport-mmio.tex b/transport-mmio.tex
index 94a93a1..042a82c 100644
--- a/transport-mmio.tex
+++ b/transport-mmio.tex
@@ -242,6 +242,14 @@ \subsection{MMIO Device Register Layout}\label{sec:Virtio Transport Options / Vi
     apply to the queue selected by writing to \field{QueueSel}.
   }
   \hline
+  \mmioreg{SHMPageShift}{Shared memory region page shift 8 bit long}{0x0c4}{R}{%
+    Reading from this register returns the page shift derived from the supported
+    page size for the memory region selected by the \field{SHMSel} register. The
+    page shift is derived from the page size by using this formula:
+    $page size = 1 << (page shift + 12)$.
+    See also \ref {sec:Basic Facilities of a Virtio Device / Shared Memory Regions / Page alignment restrictions}.
+  }
+  \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.
-- 
2.49.0