soc/intel_adsp: cavstool: add support for DSP power state: D3

Change some behaviors when --log-only is passed in order to add support
for DSP power state: D3. This makes it possible to keep `cavstool
--log-only` running permanently in the "real-world" use case where the
Linux kernel loads the firmware and powers down audio when not in use.

More specifically:
- Do not disable D3 when using --log-only.
- Wait forever for the FW at boot time.
- Check live status when an invalid IPC is received and wait forever if
  not alive.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

soc/xtensa/intel_adsp/tools/cavstool.py

@@ -230,10 +230,10 @@ def map_regs():
         else:
             log.warning(found_msg + ", unloading module")
             runx(f"rmmod -f {mod}")
-
-    # Disengage runtime power management so the kernel doesn't put it to sleep
-    with open(f"{pcidir}/power/control", "w") as ctrl:
-        ctrl.write("on")
+            # Disengage runtime power management so the kernel doesn't put it to sleep
+            log.info(f"Forcing {pcidir}/power/control to always 'on'")
+            with open(f"{pcidir}/power/control", "w") as ctrl:
+                ctrl.write("on")
 
     # Make sure PCI memory space access and busmastering are enabled.
     # Also disable interrupts so as not to confuse the kernel.
@@ -633,6 +633,15 @@ def ipc_command(data, ext_data):
             hda_str.mem.seek(0)
     else:
         log.warning(f"cavstool: Unrecognized IPC command 0x{data:x} ext 0x{ext_data:x}")
+        if not fw_is_alive():
+            if args.log_only:
+                log.info("DSP power seems off")
+                wait_fw_entered(timeout_s=None)
+            else:
+                log.warning("DSP power seems off?!")
+                time.sleep(2) # potential spam reduction
+
+            return
 
     dsp.HIPCTDR = 1<<31 # Ack local interrupt, also signals DONE on v1.5
     if cavs18:
@@ -658,7 +667,7 @@ async def _main(server):
     log.info(f"Detected cAVS {'1.5' if cavs15 else '1.8+'} hardware")
 
     if args.log_only:
-        wait_fw_entered()
+        wait_fw_entered(timeout_s=None)
     else:
         if not fw_file:
             log.error("Firmware file argument missing")