soc/integration: Add LiteXSocArgumentParser to be able to expose CPU parameters to user on targets.

Currently used for CPU parameters could problably be extented to simplify other parts
of the code in the future.

litex/soc/integration/soc.py

@@ -1,7 +1,7 @@
 #
 # This file is part of LiteX.
 #
-# This file is Copyright (c) 2014-2021 Florent Kermarrec <florent@enjoy-digital.fr>
+# This file is Copyright (c) 2014-2022 Florent Kermarrec <florent@enjoy-digital.fr>
 # This file is Copyright (c) 2013-2014 Sebastien Bourdeauducq <sb@m-labs.hk>
 # This file is Copyright (c) 2019 Gabriel L. Somlo <somlo@cmu.edu>
 # SPDX-License-Identifier: BSD-2-Clause
@@ -9,6 +9,7 @@
 import sys
 import time
 import logging
+import argparse
 import datetime
 from math import log2, ceil
 
@@ -1894,3 +1895,27 @@ class LiteXSoC(SoC):
         self.add_constant("VIDEO_FRAMEBUFFER_VRES", vres)
         self.add_constant("VIDEO_FRAMEBUFFER_DEPTH", vfb.depth)
 
+# LiteXSoCArgumentParser ---------------------------------------------------------------------------
+
+class LiteXSoCArgumentParser(argparse.ArgumentParser):
+    def parse_args(self):
+
+        def get_selected_cpu_name():
+            for name, cpu_cls in cpu.CPUS.items():
+                if f"--cpu-type={name}" in sys.argv: # FIXME: Improve.
+                    return cpu_cls
+            return None
+
+        # Intercept selected CPU to fill arguments.
+        cpu_cls = get_selected_cpu_name()
+        if cpu_cls is not None and hasattr(cpu_cls, "args_fill"):
+            cpu_cls.args_fill(self)
+
+        # Get Command-line arguments.
+        args = argparse.ArgumentParser.parse_args(self)
+
+        # Re-inject CPU read arguments.
+        if cpu_cls is not None and hasattr(cpu_cls, "args_read"):
+            cpu_cls.args_read(args)
+
+        return args