arch-vega: Bypass Ruby for functional page walks

Currently if a Ruby functional access fails to find an address in the
caches, it gives up. For functional page table walks we need to be able
to go all the way to memory. This adds a pointer to the system object
which allows the walker to get a pointer to device memory which can be
used to do a functional access directly to memory bypassing Ruby.

Change-Id: I0ead6e5e130a0d53021c44ae9221b167c6316ab2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57529
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/amdgpu/vega/pagetable_walker.cc

@@ -34,6 +34,7 @@
 #include <memory>
 
 #include "arch/amdgpu/vega/faults.hh"
+#include "mem/abstract_mem.hh"
 #include "mem/packet_access.hh"
 
 namespace gem5
@@ -84,7 +85,9 @@ Walker::WalkerState::startFunctional(Addr base, Addr vaddr,
         DPRINTF(GPUPTWalker, "Sending functional read to %#lx\n",
                 read->getAddr());
 
-        walker->port.sendFunctional(read);
+        auto devmem = walker->system->getDeviceMemory(read);
+        assert(devmem);
+        devmem->access(read);
 
         fault = stepWalk();
         assert(fault == NoFault || read == NULL);

src/arch/amdgpu/vega/pagetable_walker.hh

@@ -179,6 +179,9 @@ class Walker : public ClockedObject
     void walkerResponse(WalkerState *state, VegaTlbEntry& entry,
                         PacketPtr pkt);
 
+    // System pointer for functional accesses
+    System *system;
+
   public:
     void setTLB(GpuTLB * _tlb)
     {
@@ -191,7 +194,7 @@ class Walker : public ClockedObject
         port(name() + ".port", this),
         funcState(this, nullptr, true), tlb(nullptr),
         requestorId(p.system->getRequestorId(this)),
-        deviceRequestorId(999)
+        deviceRequestorId(999), system(p.system)
     {
         DPRINTF(GPUPTWalker, "Walker::Walker %p\n", this);
     }