Clean up fespi flashing code (#313)

* WIP upstream review feedback.

See http://openocd.zylin.com/#/c/4656/

The main change is to get rid of macros that contain a return statement.

Change-Id: Iff79a8aa7c40ee04a8d1f07d973f9b29d4899d5c

* Remove unaligned head/tail code.

From inspection it's not clear to me that this is necessary at all. I've
been unable to make a test case that results in anything besides a
4-byte aligned flash to happen. Sections that aren't multiples of 4 are
common, and appear to work fine.

Change-Id: Idb6109ca015ae06b9d8f16bd883f9c8f5c51087d

* Move fespi native code into contrib/loaders

As suggested by http://openocd.zylin.com/#/c/4656/

Change-Id: I275012aa8a1ef6a0e8a2ec8ebe8643d87de24407

* Reenable hw mode if errors happen without it.

Change-Id: I1220033c13d02e8a441992bd6daa0ec3b5acbfca

* Default flash to not protected.

Requested by upstream review.

Change-Id: I61753bd9909d7f21ef6624037a865072c18bd1d8

contrib/loaders/flash/fespi/Makefile

@@ -0,0 +1,28 @@
+BIN2C = ../../../../src/helper/bin2char.sh
+
+CROSS_COMPILE ?= riscv64-unknown-elf-
+
+CC=$(CROSS_COMPILE)gcc
+OBJCOPY=$(CROSS_COMPILE)objcopy
+OBJDUMP=$(CROSS_COMPILE)objdump
+
+CFLAGS = -march=rv32i -mabi=ilp32 -x assembler-with-cpp - -nostdlib -nostartfiles
+
+all: fespi.inc
+
+.PHONY: clean
+
+%.elf: %.S
+	$(CC) $(CFLAGS) $< -o $@
+
+%.lst: %.elf
+	$(OBJDUMP) -S $< > $@
+
+%.bin: %.elf
+	$(OBJCOPY) -Obinary $< $@
+
+%.inc: %.bin
+	$(BIN2C) < $< > $@
+
+clean:
+	-rm -f *.elf *.lst *.bin *.inc

contrib/loaders/flash/fespi/fespi.S

@@ -0,0 +1,99 @@
+#define SPIFLASH_READ_STATUS	0x05 // Read Status Register
+#define SPIFLASH_BSY_BIT		0x00000001 // WIP Bit of SPI SR on SMI SR
+
+// Register offsets
+#define FESPI_REG_FMT             0x40
+#define FESPI_REG_TXFIFO          0x48
+#define FESPI_REG_RXFIFO          0x4c
+#define FESPI_REG_IP              0x74
+
+// Fields
+#define FESPI_IP_TXWM             0x1
+#define FESPI_FMT_DIR(x)          (((x) & 0x1) << 3)
+
+// To enter, jump to the start of command_table (ie. offset 0).
+//      a0 - FESPI base address
+//      a1 - start address of buffer
+
+// The buffer contains a "program" in byte sequences. The first byte in a
+// sequence determines the operation. Some operation will read more data from
+// the program, while some will not. The operation byte is the offset into
+// command_table, so eg. 4 means exit, 8 means transmit, and so on.
+
+		.global _start
+_start:
+command_table:
+		j       main            // 0
+		ebreak                  // 4
+		j       tx              // 8
+		j       txwm_wait       // 12
+		j       write_reg       // 16
+		j		wip_wait		// 20
+		j		set_dir			// 24
+
+// Execute the program.
+main:
+		lbu     t0, 0(a1)
+		addi    a1, a1, 1
+		la      t1, command_table
+		add     t0, t0, t1
+		jr      t0
+
+// Read 1 byte the contains the number of bytes to transmit. Then read those
+// bytes from the program and transmit them one by one.
+tx:
+		lbu     t1, 0(a1)       // read number of bytes to transmit
+		addi    a1, a1, 1
+1:      lw      t0, FESPI_REG_TXFIFO(a0)        // wait for FIFO clear
+		bltz    t0, 1b
+		lbu     t0, 0(a1)       // Load byte to write
+		sw      t0, FESPI_REG_TXFIFO(a0)
+		addi    a1, a1, 1
+		addi    t1, t1, -1
+		bgtz    t1, 1b
+		j       main
+
+// Wait until TXWM is set.
+txwm_wait:
+1:      lw      t0, FESPI_REG_IP(a0)
+		andi    t0, t0, FESPI_IP_TXWM
+		beqz    t0, 1b
+		j       main
+
+// Read 1 byte that contains the offset of the register to write, and 1 byte
+// that contains the data to write.
+write_reg:
+		lbu     t0, 0(a1)       // read register to write
+		add     t0, t0, a0
+		lbu     t1, 1(a1)       // read value to write
+		addi    a1, a1, 2
+		sw      t1, 0(t0)
+		j       main
+
+wip_wait:
+		li		a2, SPIFLASH_READ_STATUS
+		jal		txrx_byte
+		// discard first result
+1:		li		a2, 0
+		jal		txrx_byte
+		andi	t0, a2, SPIFLASH_BSY_BIT
+		bnez	t0, 1b
+		j		main
+
+txrx_byte:	// transmit the byte in a2, receive a bit into a2
+		lw      t0, FESPI_REG_TXFIFO(a0)        // wait for FIFO clear
+		bltz    t0, txrx_byte
+		sw      a2, FESPI_REG_TXFIFO(a0)
+1:		lw		a2, FESPI_REG_RXFIFO(a0)
+		bltz	a2, 1b
+		ret
+
+set_dir:
+		lw		t0, FESPI_REG_FMT(a0)
+		li		t1, ~(FESPI_FMT_DIR(0xFFFFFFFF))
+		and		t0, t0, t1
+		lbu     t1, 0(a1)       // read value to OR in
+		addi    a1, a1, 1
+		or		t0, t0, t1
+		sw		t0, FESPI_REG_FMT(a0)
+		j		main

contrib/loaders/flash/fespi/fespi.inc

@@ -0,0 +1,15 @@
+/* Autogenerated with ../../../../src/helper/bin2char.sh */
+0x6f,0x00,0xc0,0x01,0x73,0x00,0x10,0x00,0x6f,0x00,0xc0,0x02,0x6f,0x00,0x00,0x05,
+0x6f,0x00,0xc0,0x05,0x6f,0x00,0x00,0x07,0x6f,0x00,0x00,0x0a,0x83,0xc2,0x05,0x00,
+0x93,0x85,0x15,0x00,0x17,0x03,0x00,0x00,0x13,0x03,0xc3,0xfd,0xb3,0x82,0x62,0x00,
+0x67,0x80,0x02,0x00,0x03,0xc3,0x05,0x00,0x93,0x85,0x15,0x00,0x83,0x22,0x85,0x04,
+0xe3,0xce,0x02,0xfe,0x83,0xc2,0x05,0x00,0x23,0x24,0x55,0x04,0x93,0x85,0x15,0x00,
+0x13,0x03,0xf3,0xff,0xe3,0x44,0x60,0xfe,0x6f,0xf0,0x5f,0xfc,0x83,0x22,0x45,0x07,
+0x93,0xf2,0x12,0x00,0xe3,0x8c,0x02,0xfe,0x6f,0xf0,0x5f,0xfb,0x83,0xc2,0x05,0x00,
+0xb3,0x82,0xa2,0x00,0x03,0xc3,0x15,0x00,0x93,0x85,0x25,0x00,0x23,0xa0,0x62,0x00,
+0x6f,0xf0,0xdf,0xf9,0x13,0x06,0x50,0x00,0xef,0x00,0x80,0x01,0x13,0x06,0x00,0x00,
+0xef,0x00,0x00,0x01,0x93,0x72,0x16,0x00,0xe3,0x9a,0x02,0xfe,0x6f,0xf0,0x1f,0xf8,
+0x83,0x22,0x85,0x04,0xe3,0xce,0x02,0xfe,0x23,0x24,0xc5,0x04,0x03,0x26,0xc5,0x04,
+0xe3,0x4e,0x06,0xfe,0x67,0x80,0x00,0x00,0x83,0x22,0x05,0x04,0x13,0x03,0x70,0xff,
+0xb3,0xf2,0x62,0x00,0x03,0xc3,0x05,0x00,0x93,0x85,0x15,0x00,0xb3,0xe2,0x62,0x00,
+0x23,0x20,0x55,0x04,0x6f,0xf0,0x9f,0xf4,