soc/cores/spi: make dynamic clk divider optional (can be enabled with…

… add_clk_divider method) and only use it in add_spi_sdcard.

litex/soc/cores/spi.py

@@ -137,20 +137,22 @@ def add_csr(self):
             CSRField("sel", len(self.cs), reset=1, description="Write ``1`` to corresponding bit to enable Xfer for chip.")
         ], description="SPI Chip Select.")
         self._loopback = CSRStorage(description="SPI loopback mode.\n\n Write ``1`` to enable MOSI to MISO internal loopback.")
-        self._clk_divider = CSRStorage(16, description="SPI Clk Divider.", reset=self.clk_divider.reset)
 
         self.comb += [
             self.start.eq(self._control.fields.start),
             self.length.eq(self._control.fields.length),
             self.mosi.eq(self._mosi.storage),
             self.cs.eq(self._cs.storage),
             self.loopback.eq(self._loopback.storage),
-            self.clk_divider.eq(self._clk_divider.storage),
 
             self._status.fields.done.eq(self.done),
             self._miso.status.eq(self.miso),
         ]
 
+    def add_clk_divider(self):
+        self._clk_divider = CSRStorage(16, description="SPI Clk Divider.", reset=self.clk_divider.reset)
+        self.comb += self.clk_divider.eq(self._clk_divider.storage)
+
 # SPI Slave ----------------------------------------------------------------------------------------
 
 class SPISlave(Module):

litex/soc/integration/soc.py

@@ -1154,5 +1154,6 @@ def add_spi_sdcard(self, name="spisdcard", clk_freq=400e3):
         if hasattr(pads, "rst"):
             self.comb += pads.rst.eq(0)
         spisdcard = SPIMaster(pads, 8, self.sys_clk_freq, 400e3)
+        spisdcard.add_clk_divider()
         setattr(self.submodules, name, spisdcard)
         self.add_csr(name)