soc/cores/gpio: add dts support

gpio will require target integration, for example:

    self.gpio = gpio = GPIOTristate(pads = pads)
    self.add_dts_node("gpio", gpio)

NOTE: GPIOIn and GPIOOut will generate DTS compatible with the current
Linux driver, but the existing DTS nodes for litex GPIO depart from
DTS conventions are are worth changing if there are no compatibility
concerns.

litex/soc/cores/gpio.py

@@ -8,7 +8,7 @@
 from migen import *
 from migen.genlib.cdc import MultiReg
 
-from litex.gen import *
+from litex.gen import dts_property, LiteXModule
 
 from litex.soc.interconnect.csr import *
 from litex.soc.interconnect.csr_eventmanager import *
@@ -46,21 +46,48 @@ class _GPIOIRQ(LiteXModule):
 # GPIO Input ---------------------------------------------------------------------------------------
 
 class GPIOIn(_GPIOIRQ):
-    def __init__(self, pads, with_irq=False):
+    dts_compatible = "litex,gpioin"
+    dts_node = "gpio"
+    dts_properties = dts_property("gpio-controller")
+    dts_properties += dts_property("#gpio-cells", 2)
+
+    def __init__(self, pads, with_irq=False, deprecated_dts=True):
         pads = _to_signal(pads)
         self._in = CSRStatus(len(pads), description="GPIO Input(s) Status.")
         self.specials += MultiReg(pads, self._in.status)
+
+        self.dts_properties += dts_property("ngpio", len(pads))
+        if deprecated_dts:  # deprecated: for linux driver
+            # the values below are based on json2dts_linux "switches"
+            # should be compatible with the linux driver
+            self.dts_compatible = ["litex,gpioin", "litex,gpio"]
+            self.dts_properties += dts_property("litex,direction", "in")
+            self.dts_properties += dts_property("litex,ngpio", len(pads))
+
         if with_irq:
             self.add_irq(self._in.status)
 
 # GPIO Output --------------------------------------------------------------------------------------
 
 class GPIOOut(LiteXModule):
-    def __init__(self, pads, reset=0):
+    dts_compatible = "litex,gpioout"
+    dts_node = "gpio"
+    dts_properties = dts_property("gpio-controller")
+    dts_properties += dts_property("#gpio-cells", 2)
+
+    def __init__(self, pads, reset=0, deprecated_dts=True):
         pads = _to_signal(pads)
         self.out = CSRStorage(len(pads), reset=reset, description="GPIO Output(s) Control.")
         self.comb += pads.eq(self.out.storage)
 
+        self.dts_properties += dts_property("ngpio", len(pads))
+        if deprecated_dts: # deprecated: for linux driver
+            # the values below are based on json2dts_linux "leds"
+            # should be compatible with the linux driver
+            self.dts_compatible = ["litex,gpioout", "litex,gpio"]
+            self.dts_properties += dts_property("litex,direction", "out")
+            self.dts_properties += dts_property("litex,ngpio", len(pads))
+
 # GPIO Input/Output --------------------------------------------------------------------------------
 
 class GPIOInOut(LiteXModule):
@@ -74,6 +101,11 @@ class GPIOInOut(LiteXModule):
 # GPIO Tristate ------------------------------------------------------------------------------------
 
 class GPIOTristate(_GPIOIRQ):
+    dts_compatible = "litex,gpiotristate"
+    dts_node = "gpio"
+    dts_properties = dts_property("gpio-controller")
+    dts_properties += dts_property("#gpio-cells", 2)
+
     def __init__(self, pads, with_irq=False):
         internal = not (hasattr(pads, "o") and hasattr(pads, "oe") and hasattr(pads, "i"))
         nbits    = len(pads) if internal else len(pads.o)
@@ -104,5 +136,7 @@ class GPIOTristate(_GPIOIRQ):
                 self.comb += pads.o[i].eq(self._out.storage[i])
                 self.specials += MultiReg(pads.i[i], self._in.status[i])
 
+        self.dts_properties += dts_property("ngpio", nbits)
+
         if with_irq:
             self.add_irq(self._in.status)