mem: Add a class to describe a back door request.

In cases where a back door is not being requested alongside a packet
or request, there needs to be a structure which describes the address
range to use, and what type of access the back door should support. It
would be possible to make a Packet/Request to carry that information,
but those types are actually pretty big, and have a lot of extra
overhead which would be overkill for this purpose.

Change-Id: I3638361ffa758ee959cb3bc57f7c35f2aa34a36c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65751
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/backdoor.hh

@@ -126,6 +126,25 @@ class MemBackdoor
 
 typedef MemBackdoor *MemBackdoorPtr;
 
+class MemBackdoorReq
+{
+  private:
+    AddrRange _range;
+    MemBackdoor::Flags _flags;
+
+  public:
+    MemBackdoorReq(AddrRange r, MemBackdoor::Flags new_flags) :
+        _range(r), _flags(new_flags)
+    {}
+
+    const AddrRange &range() const { return _range; }
+
+    bool readable() const { return _flags & MemBackdoor::Readable; }
+    bool writeable() const { return _flags & MemBackdoor::Writeable; }
+
+    MemBackdoor::Flags flags() const { return _flags; }
+};
+
 } // namespace gem5
 
 #endif  //__MEM_BACKDOOR_HH__