mini.hv.dcp: Decode common messages

This accounts for most of the DCP traffic once macOS is booted. I used
a sophisticated side-channel hypervisor timing attack to determine the
message functions [ adding time.sleep(1) ]

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>

proxyclient/hv/trace_dcp.py

@@ -2,8 +2,54 @@
 
 trace_device("/arm-io/dcp", True, ranges=[1])
 
-from m1n1.trace.asc import ASCTracer
+from m1n1.trace.asc import ASCTracer, msg, msg_log, DIR
 
 ASCTracer = ASCTracer._reloadcls()
-dcp_tracer = ASCTracer(hv, "/arm-io/dcp", verbose=1)
+
+# Sequence of commands sent to endpoint 0x37 to present a frame The new
+# framebuffer becomes visible after sending PRESENT, confirmed by timing.
+PRE_PRESENT  = 0x0000003c00000202
+PRESENT      = 0x000008b400000202
+POST_PRESENT = 0x0000000000000342
+
+# Sent repeatedly when reconfiguring the display (clicking anything in the
+# Displays section of System Preferences -- scaling, rotation, colour profile,
+# all included). The actual command is in shared memory. Acked by the DCP with
+# an OK. This command is _not_ sufficient for hardware resolution changes, only
+# for software (perceived) changes.
+RECONFIGURE  = 0x0000106c00000202
+
+# Response to pre_present, present, reconfigure
+DCP_OK =    0x0000000000000242
+
+# Response to post_presnt
+PRESENT_3_RESP = 0x0000062800000302
+
+class DCPTracer(ASCTracer):
+    @msg(0x37, 0x0, None)
+    def main(self, r0, r1):
+        v = r0.value
+
+        if v == PRE_PRESENT:
+            self.log(f"Pre present")
+            return True
+        elif v == PRESENT:
+            self.log(f"Present")
+            return True
+        elif v == POST_PRESENT:
+            self.log(f"Post present")
+            return True
+        elif v == RECONFIGURE:
+            self.log(f"Reconfiguring")
+            return True
+        elif v == DCP_OK:
+            # Just noise, don't bother printing
+            return True
+        elif v == PRESENT_3_RESP:
+            self.log(f"Frame presented")
+            return True
+        else:
+            return False
+
+dcp_tracer = DCPTracer(hv, "/arm-io/dcp", verbose=1)
 dcp_tracer.start()