make/soc_linux: add SPI SDCard support and enable it on Nexys4DDR/De1…

…0Nano(MiSTer).

To boot Linux from the SDCard:

Use a FAT16 partition on SDCard and copy the images to it:
- Image from buildroot/Image.
- rootfs.cpio fom buildroot/rootfs.cpio.
- rv32.dtb from buildroot/rv32.dtb.
- emulator.bin emulator/emulator.bin.

Then use the spisdcardboot command of the LiteX bios.

make.py

@@ -132,7 +132,7 @@ def load(self):
 class Nexys4DDR(Board):
     def __init__(self):
         from litex_boards.targets import nexys4ddr
-        Board.__init__(self, nexys4ddr.EthernetSoC, {"serial", "ethernet"})
+        Board.__init__(self, nexys4ddr.EthernetSoC, {"serial", "spisdcard", "ethernet"})
 
     def load(self):
         from litex.build.xilinx import VivadoProgrammer
@@ -246,7 +246,7 @@ def load(self):
 class De10Nano(Board):
     def __init__(self):
         from litex_boards.targets import de10nano
-        Board.__init__(self, de10nano.MiSTerSDRAMSoC, {"serial", "leds", "switches"})
+        Board.__init__(self, de10nano.MiSTerSDRAMSoC, {"serial", "spisdcard", "leds", "switches"})
 
     def load(self):
         from litex.build.altera import USBBlaster
@@ -329,6 +329,8 @@ def main():
             soc.add_spi_flash(dummy_cycles=board.SPIFLASH_DUMMY_CYCLES)
             soc.add_constant("SPIFLASH_PAGE_SIZE", board.SPIFLASH_PAGE_SIZE)
             soc.add_constant("SPIFLASH_SECTOR_SIZE", board.SPIFLASH_SECTOR_SIZE)
+        if "spisdcard" in board.soc_capabilities:
+            soc.add_spi_sdcard()
         if "ethernet" in board.soc_capabilities:
             soc.configure_ethernet(local_ip=args.local_ip, remote_ip=args.remote_ip)
         if "leds" in board.soc_capabilities:

soc_linux.py

@@ -116,6 +116,13 @@ def add_spi_flash(self, dummy_cycles):
             self.add_wb_slave(self.mem_map["spiflash"], self.spiflash.bus)
             self.add_csr("spiflash")
 
+        def add_spi_sdcard(self, spisdcard_clk_freq=400e3):
+            spisdcard_pads = self.platform.request("spisdcard")
+            if hasattr(spisdcard_pads, "rst"):
+                self.comb += spisdcard_pads.rst.eq(0)
+            self.submodules.spisdcard = SPIMaster(spisdcard_pads, 8, self.clk_freq, spisdcard_clk_freq)
+            self.add_csr("spisdcard")
+
         def add_leds(self):
             self.submodules.leds = GPIOOut(Cat(platform_request_all(self.platform, "user_led")))
             self.add_csr("leds")