Add Linux loader

This privdes just enough firmware to load Linux. The loader is linked to
run from the aliased BRAM address.

It can load a raw kernel (vmlinux.bin) or a wrapper that embeds the
device tree (dtbImage.microwatt).

The printf comes from https://github.com/mpredfearn/simple-printf

 1. Build Linux for microwatt
  objcopy -O binary microwatt/vmlinux vmlinux.bin

 2. Build a dtb

 3. Set MW_DEBUG to point to a copy of mw_debug and type `make load` to
    load the loader into BRAM.

 4. Press 'RESET'

 5. Follow the instructions:

	Microwatt Loader (Jun  2 2020 21:31:16)

	Load binaries into SDRAM and select option to start:

	vmlinux.bin and dtb:
	 mw_debug -b jtag stop load vmlinux.bin load microwatt.dtb 1000000 start
	 press 'l' to start'

	dtbImage.microwatt:
	 mw_debug -b jtag stop load dtbImage.microwatt 500000 start
	 press 'w' to start'

If you want to test other software, such as MicroPython, you can also
load it to the start of SDRAM and the loader will jump to it with 'l'.

Signed-off-by: Joel Stanley <[email protected]>

.gitignore

@@ -3,8 +3,17 @@
 *.cf
 *.s
 *_tb
+*.swp
 main_ram.bin
 tests/*/*.bin
 tests/*/*.hex
 tests/*/*.elf
 TAGS
+tags
+scripts/mw_debug/mw_debug
+loader/loader.bin
+loader/loader.hex
+loader/loader.elf
+loader/powerpc.lds
+*.swn
+*.swo

loader/Makefile

@@ -0,0 +1,41 @@
+ARCH = $(shell uname -m)
+ifneq ("$(ARCH)", "ppc64")
+ifneq ("$(ARCH)", "ppc64le")
+	CROSS_COMPILE ?= powerpc64le-linux-gnu-
+endif
+endif
+
+PYTHON3 ?= python3
+MW_DEBUG ?= mw_debug
+BRAM_ADDRESS ?= 0x80000000
+
+CC = $(CROSS_COMPILE)gcc
+LD = $(CROSS_COMPILE)ld
+OBJCOPY = $(CROSS_COMPILE)objcopy
+
+CFLAGS = -Os -g -Wall -std=c99 -msoft-float -mno-string -mno-multiple \
+	 -mno-vsx -mno-altivec -mlittle-endian -fno-stack-protector \
+	 -mstrict-align -ffreestanding -fdata-sections -ffunction-sections \
+	 -I../include
+ASFLAGS = $(CFLAGS)
+LDFLAGS = -T powerpc.lds --gc-sections
+
+all: loader.hex
+
+load: loader.bin
+	$(MW_DEBUG) -b jtag load $^ $(BRAM_ADDRESS)
+
+%.lds : %.lds.S
+	$(CC) -I../include -P -E $< -o $@
+
+loader.elf: loader.o head.o ../lib/console.o load.o printf.o | powerpc.lds
+	$(LD) $(LDFLAGS) -o $@ $^
+
+loader.bin: loader.elf
+	$(OBJCOPY) -O binary $^ $@
+
+loader.hex: loader.bin
+	$(PYTHON3) ../scripts/bin2hex.py $^ > $@
+
+clean:
+	@rm -f *.o loader.elf loader.bin loader.hex powerpc.lds

loader/head.S

@@ -0,0 +1,109 @@
+/* Copyright 2013-2014 IBM Corp.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * 	http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <microwatt_soc.h>
+
+#define STACK_TOP (BRAM_BASE + 0x2000)
+
+#define FIXUP_ENDIAN						   \
+	tdi   0,0,0x48;	  /* Reverse endian of b . + 8		*/ \
+	b     191f;	  /* Skip trampoline if endian is good	*/ \
+	.long 0xa600607d; /* mfmsr r11				*/ \
+	.long 0x01006b69; /* xori r11,r11,1			*/ \
+	.long 0x05009f42; /* bcl 20,31,$+4			*/ \
+	.long 0xa602487d; /* mflr r10				*/ \
+	.long 0x14004a39; /* addi r10,r10,20			*/ \
+	.long 0xa64b5a7d; /* mthsrr0 r10			*/ \
+	.long 0xa64b7b7d; /* mthsrr1 r11			*/ \
+	.long 0x2402004c; /* hrfid				*/ \
+191:
+
+
+/* Load an immediate 64-bit value into a register */
+#define LOAD_IMM64(r, e)			\
+	lis     r,(e)@highest;			\
+	ori     r,r,(e)@higher;			\
+	rldicr  r,r, 32, 31;			\
+	oris    r,r, (e)@h;			\
+	ori     r,r, (e)@l;
+
+	.section ".head","ax"
+
+	/*
+	 * Microwatt currently enters in LE mode at 0x0, so we don't need to
+	 * do any endian fix ups>
+	 */
+	. = 0
+.global _start
+_start:
+	b	boot_entry
+
+	/* QEMU enters at 0x10 */
+	. = 0x10
+	FIXUP_ENDIAN
+	b	boot_entry
+
+	. = 0x100
+	FIXUP_ENDIAN
+	b	boot_entry
+
+.global boot_entry
+boot_entry:
+	/* setup stack */
+	LOAD_IMM64(%r1, STACK_TOP - 0x100)
+	LOAD_IMM64(%r12, main)
+	mtctr	%r12,
+	bctrl
+	b .
+
+#define EXCEPTION(nr)		\
+	.= nr			;\
+	b	.
+
+	/* More exception stubs */
+	EXCEPTION(0x300)
+	EXCEPTION(0x380)
+	EXCEPTION(0x400)
+	EXCEPTION(0x480)
+	EXCEPTION(0x500)
+	EXCEPTION(0x600)
+	EXCEPTION(0x700)
+	EXCEPTION(0x800)
+	EXCEPTION(0x900)
+	EXCEPTION(0x980)
+	EXCEPTION(0xa00)
+	EXCEPTION(0xb00)
+	EXCEPTION(0xc00)
+	EXCEPTION(0xd00)
+	EXCEPTION(0xe00)
+	EXCEPTION(0xe20)
+	EXCEPTION(0xe40)
+	EXCEPTION(0xe60)
+	EXCEPTION(0xe80)
+	EXCEPTION(0xf00)
+	EXCEPTION(0xf20)
+	EXCEPTION(0xf40)
+	EXCEPTION(0xf60)
+	EXCEPTION(0xf80)
+#if 0
+	EXCEPTION(0x1000)
+	EXCEPTION(0x1100)
+	EXCEPTION(0x1200)
+	EXCEPTION(0x1300)
+	EXCEPTION(0x1400)
+	EXCEPTION(0x1500)
+	EXCEPTION(0x1600)
+#endif

loader/load.S

@@ -0,0 +1,26 @@
+/*
+ * Set up system for jumping to Linux.
+ *
+ * load_linux(kernel, dtb)
+ */
+.global load_linux
+load_linux:
+	/* ABI:
+	 *  r5: zero (no openfirmware)
+	 *  r3: device tree
+	 */
+	addi	%r5,0,0
+	addi	%r12,%r3,0
+	addi	%r3,%r4,0
+	mtctr	%r12
+	bctrl
+	b .
+
+/*
+ * Invalidate the icache.
+ */
+.global invalidate_icache
+invalidate_icache:
+        icbi    0,0
+	isync
+	blr

loader/loader.c

@@ -0,0 +1,63 @@
+#include <stdint.h>
+#include <stdbool.h>
+#include <io.h>
+#include <microwatt_soc.h>
+
+#include "console.h"
+
+extern void load_linux(unsigned long kernel, unsigned long dtb);
+extern void invalidate_icache(void);
+
+extern int simple_printf(char *fmt, ...);
+#define printf(...) simple_printf(__VA_ARGS__)
+
+#define DTB_ADDR	0x01000000L
+
+#define DTBIMAGE_ADDR 	0x500000L
+
+int main(void)
+{
+	int i;
+	potato_uart_init();
+	unsigned long kernel, dtb;
+
+	printf("\r\nMicrowatt Loader (%s %s)\r\n\r\n", __DATE__, __TIME__);
+
+	writeq(SYS_REG_CTRL_DRAM_AT_0, SYSCON_BASE + SYS_REG_CTRL);
+	invalidate_icache();
+
+	printf("Load binaries into SDRAM and select option to start:\r\n\r\n");
+	printf("vmlinux.bin and dtb:\r\n");
+	printf(" mw_debug -b jtag stop load vmlinux.bin load microwatt.dtb %x start\r\n",
+			DTB_ADDR);
+	printf(" press 'l' to start'\r\n\r\n");
+
+	printf("dtbImage.microwatt:\r\n");
+	printf(" mw_debug -b jtag stop load dtbImage.microwatt %x start\r\n",
+			DTBIMAGE_ADDR);
+	printf(" press 'w' to start'\r\n\r\n");
+
+	while (1) {
+		switch (getchar()) {
+		case 'l':
+			kernel = 0;
+			dtb = DTB_ADDR;
+			goto load;
+		case 'w':
+			kernel = DTBIMAGE_ADDR;
+			dtb = -1;
+			goto load;
+		default:
+			continue;
+		}
+	}
+
+load:
+	printf("Loading Linux at %08x...\r\n", 0x0);
+	for (i = 0; i < 80; i++)
+		putchar('.');
+	printf("\r\n");
+	load_linux(kernel, dtb);
+
+	while (1);
+}

loader/powerpc.lds.S

@@ -0,0 +1,17 @@
+#include <microwatt_soc.h>
+
+#define BASE_ADDR	BRAM_BASE
+
+SECTIONS
+{
+	_start = .;
+	. = BASE_ADDR;
+	.head : {
+		KEEP(*(.head))
+	}
+	. = (BASE_ADDR + 0x1000);
+	.text : { *(.text) }
+	. = (BASE_ADDR + 0x2000);
+	.data : { *(.data) }
+	.bss : { *(.bss) }
+}