mpc85xx: add SPI kernel loader for TP-Link TL-WDR4900 v1

Similar to the lzma-loader on our MIPS targets, the spi-loader acts as
a second-stage loader that will then load and start the actual kernel.
As the TL-WDR4900 uses SPI-NOR and the P1010 family does not have support
for memory mapping of this type of flash, this loader needs to contain a
basic driver for the FSL ESPI controller.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

target/linux/mpc85xx/image/spi-loader/.gitignore

@@ -0,0 +1 @@
+/out

target/linux/mpc85xx/image/spi-loader/Makefile

@@ -0,0 +1,60 @@
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (C) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+
+CONFIG     ?= $(error No configuration set)
+
+include config/$(CONFIG).mk
+
+MKIMAGE    := mkimage
+KARCH      := powerpc
+CC         := $(CROSS_COMPILE)gcc
+LD         := $(CROSS_COMPILE)ld
+OBJCOPY    := $(CROSS_COMPILE)objcopy
+
+PROGRAM_NAME := MPC85xx SPI loader
+
+BIN_FLAGS  := -O binary --pad-to=$(PAD_TO)
+
+CFLAGS     += -std=gnu17 -Os -Wall -Wstrict-prototypes \
+		-fomit-frame-pointer -ffreestanding \
+		-ffunction-sections -fno-pic \
+		-Iinclude -include ../config/$(CONFIG).h \
+		-DCONFIG_PROGRAM_NAME='"$(PROGRAM_NAME)"' \
+		-DCONFIG_IMAGE_OFFSET=$(IMAGE_OFFSET)
+ASFLAGS    := $(CFLAGS)
+
+LDS        := loader.lds
+LDFLAGS    := -static --gc-sections -T $(LDS) -Ttext $(TEXT_START)
+
+OBJECTS    := head.o loader.o string.o stdio.o  drivers/serial/ns16550.o \
+		drivers/spi/fsl_espi.o drivers/spi/spi-nor.o
+
+OUTDIR     := out
+
+all: $(OUTDIR)/uImage
+
+-include $(OBJECTS:%.o=$(OUTDIR)/%.d)
+
+$(OUTDIR)/%.o: %.c Makefile config/$(CONFIG).mk
+	@mkdir -p $(dir $@)
+	$(CC) $(CFLAGS) -c -o $@ -MD -MP $<
+
+$(OUTDIR)/%.o: %.S Makefile config/$(CONFIG).mk
+	@mkdir -p $(dir $@)
+	$(CC) $(ASFLAGS) -c -o $@ -MD -MP $<
+
+$(OUTDIR)/loader.elf: $(OBJECTS:%=$(OUTDIR)/%) $(LDS)
+	$(LD) $(LDFLAGS) -o $@ $(OBJECTS:%=$(OUTDIR)/%)
+
+$(OUTDIR)/loader.bin: $(OUTDIR)/loader.elf
+	$(OBJCOPY) $(BIN_FLAGS) $< $@
+
+$(OUTDIR)/uImage: $(OUTDIR)/loader.bin
+	$(MKIMAGE) -A $(KARCH) -O linux -T kernel -C none \
+		-a $(TEXT_START) -e $(TEXT_START) -n '$(PROGRAM_NAME)' -d $< $@
+
+clean:
+	rm -rf $(OUTDIR)
+
+.PHONY: all clean

target/linux/mpc85xx/image/spi-loader/config/tplink_tl-wdr4900-v1.h

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define CONFIG_FREQ_SYSTEMBUS 399999996
+#define CONFIG_SPI_MAX_HZ 25000000
+
+#define CONFIG_SERIAL_NS16550_REG_BASE 0xffe04500
+#define CONFIG_SERIAL_NS16550_REG_SHIFT 0
+
+#define CONFIG_SPI_FSL_ESPI_REG_BASE 0xffe07000

target/linux/mpc85xx/image/spi-loader/config/tplink_tl-wdr4900-v1.mk

@@ -0,0 +1,13 @@
+TEXT_START   := 0x800000
+
+# It seems that the TP-Link TL-WDR4900 U-Boot does not flush the cache before
+# jumping into the uImage. Padding the image to 32k seems make the boot work
+# reliably.
+#
+# We leave 0x40 for the uImage header, which allows us to append the kernel
+# uImage after the loader and read with an added offset 0x8000 from the
+# SPI flash.
+PAD_TO       := 0x807fc0
+
+# Kernel begins at 0x60200 in flash, loader adds 0x8000
+IMAGE_OFFSET := 0x68200

target/linux/mpc85xx/image/spi-loader/drivers/serial/ns16550.c

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 16550 serial console support.
+ *
+ * Original copied from <file:arch/ppc/boot/common/ns16550.c>
+ * (which had no copyright)
+ * Modifications: 2006 (c) MontaVista Software, Inc.
+ *
+ * Modified by: Mark A. Greer <mgreer@mvista.com>
+ *
+ * Adapted by:
+ *
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#include <io.h>
+#include <serial.h>
+
+#define UART_DLL	0	/* Out: Divisor Latch Low */
+#define UART_DLM	1	/* Out: Divisor Latch High */
+#define UART_FCR	2	/* Out: FIFO Control Register */
+#define UART_LCR	3	/* Out: Line Control Register */
+#define UART_MCR	4	/* Out: Modem Control Register */
+#define UART_LSR	5	/* In:  Line Status Register */
+#define UART_LSR_THRE	0x20	/* Transmit-hold-register empty */
+#define UART_LSR_DR	0x01	/* Receiver data ready */
+#define UART_MSR	6	/* In:  Modem Status Register */
+#define UART_SCR	7	/* I/O: Scratch Register */
+
+static uint8_t *const reg_base = (uint8_t *)CONFIG_SERIAL_NS16550_REG_BASE;
+static const int reg_shift = CONFIG_SERIAL_NS16550_REG_SHIFT;
+
+void serial_console_putchar(char c)
+{
+	while ((in_8(reg_base + (UART_LSR << reg_shift)) & UART_LSR_THRE) == 0);
+	out_8(reg_base, c);
+}
+
+int serial_console_getc(void)
+{
+	while ((in_8(reg_base + (UART_LSR << reg_shift)) & UART_LSR_DR) == 0);
+	return in_8(reg_base);
+}
+
+int serial_console_tstc(void)
+{
+	return ((in_8(reg_base + (UART_LSR << reg_shift)) & UART_LSR_DR) != 0);
+}
+
+void serial_console_init(void)
+{
+	out_8(reg_base + (UART_FCR << reg_shift), 0x06);
+}

target/linux/mpc85xx/image/spi-loader/drivers/spi/fsl_espi.c

@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * eSPI controller driver.
+ *
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ *
+ * Based on U-Boot code:
+ *
+ * Copyright 2010-2011 Freescale Semiconductor, Inc.
+ * Copyright 2020 NXP
+ * Author: Mingkai Hu (Mingkai.hu@freescale.com)
+ *	   Chuanhua Han (chuanhua.han@nxp.com)
+ */
+
+#include <io.h>
+#include <stdio.h>
+#include <spi.h>
+
+/* eSPI Registers */
+typedef struct ccsr_espi {
+	uint32_t mode;       /* eSPI mode */
+	uint32_t event;      /* eSPI event */
+	uint32_t mask;       /* eSPI mask */
+	uint32_t com;        /* eSPI command */
+	uint32_t tx;         /* eSPI transmit FIFO access */
+	uint32_t rx;         /* eSPI receive FIFO access */
+	uint8_t  res1[8];    /* reserved */
+	uint32_t csmode[4];  /* 0x2c: sSPI CS0/1/2/3 mode */
+	uint8_t  res2[4048]; /* fill up to 0x1000 */
+} ccsr_espi_t;
+
+struct fsl_spi {
+	ccsr_espi_t	*espi;
+	uint32_t	cs;
+	uint32_t	div16;
+	uint32_t	pm;
+	uint32_t	mode;
+};
+
+#define ESPI_MAX_CS_NUM		4
+#define ESPI_FIFO_WIDTH_BIT	32
+
+#define ESPI_EV_RNE		BIT(9)
+#define ESPI_EV_TNF		BIT(8)
+#define ESPI_EV_DON		BIT(14)
+#define ESPI_EV_TXE		BIT(15)
+#define ESPI_EV_RFCNT_SHIFT	24
+#define ESPI_EV_RFCNT_MASK	(0x3f << ESPI_EV_RFCNT_SHIFT)
+
+#define ESPI_MODE_EN		BIT(31)	/* Enable interface */
+#define ESPI_MODE_TXTHR(x)	((x) << 8)	/* Tx FIFO threshold */
+#define ESPI_MODE_RXTHR(x)	((x) << 0)	/* Rx FIFO threshold */
+
+#define ESPI_COM_CS(x)		((x) << 30)
+#define ESPI_COM_TRANLEN(x)	((x) << 0)
+
+#define ESPI_CSMODE_CI_INACTIVEHIGH	BIT(31)
+#define ESPI_CSMODE_CP_BEGIN_EDGCLK	BIT(30)
+#define ESPI_CSMODE_REV_MSB_FIRST	BIT(29)
+#define ESPI_CSMODE_DIV16		BIT(28)
+#define ESPI_CSMODE_PM(x)		((x) << 24)
+#define ESPI_CSMODE_POL_ASSERTED_LOW	BIT(20)
+#define ESPI_CSMODE_LEN(x)		((x) << 16)
+#define ESPI_CSMODE_CSBEF(x)		((x) << 12)
+#define ESPI_CSMODE_CSAFT(x)		((x) << 8)
+#define ESPI_CSMODE_CSCG(x)		((x) << 3)
+
+#define ESPI_CSMODE_INIT_VAL (ESPI_CSMODE_POL_ASSERTED_LOW | \
+		ESPI_CSMODE_CSBEF(0) | ESPI_CSMODE_CSAFT(0) | \
+		ESPI_CSMODE_CSCG(1))
+
+#define ESPI_MAX_DATA_TRANSFER_LEN 0x10000
+
+static int espi_xfer(struct fsl_spi *fsl, const struct spi_transfer *msg, int n)
+{
+	ccsr_espi_t *espi = fsl->espi;
+	size_t len = spi_message_len(msg, n);
+
+	if (len > ESPI_MAX_DATA_TRANSFER_LEN)
+		return -1;
+
+	/* clear the RXCNT and TXCNT */
+	out_be32(&espi->mode, in_be32(&espi->mode) & (~ESPI_MODE_EN));
+	out_be32(&espi->mode, in_be32(&espi->mode) | ESPI_MODE_EN);
+	out_be32(&espi->com, ESPI_COM_CS(fsl->cs) | ESPI_COM_TRANLEN(len - 1));
+
+	int last_msg = n - 1;
+	int tx_msg = -1, rx_msg = -1;
+	size_t tx_len = 0, rx_len = 0, tx_pos = 0, rx_pos = 0;
+
+	while (true) {
+		if (tx_pos == tx_len && tx_msg < last_msg) {
+			tx_msg++;
+			tx_pos = 0;
+			tx_len = msg[tx_msg].len;
+		}
+		if (rx_pos == rx_len && rx_msg < last_msg) {
+			rx_msg++;
+			rx_pos = 0;
+			rx_len = msg[rx_msg].len;
+		}
+		if (rx_pos == rx_len)
+			break;
+
+		const uint8_t *tx_buf = msg[tx_msg].tx_buf;
+		uint8_t *rx_buf = msg[rx_msg].rx_buf;
+
+		uint32_t event = in_be32(&espi->event);
+
+		/* TX */
+		if ((event & ESPI_EV_TNF) && tx_len > 0) {
+			uint8_t v = 0;
+			if (tx_buf)
+				v = tx_buf[tx_pos];
+			out_8((uint8_t *)&espi->tx, v);
+			tx_pos++;
+		}
+
+		/* RX */
+		if (event & ESPI_EV_RNE) {
+			uint8_t v = in_8((uint8_t *)&espi->rx);
+			if (rx_buf)
+				rx_buf[rx_pos] = v;
+			rx_pos++;
+		}
+	}
+
+	return 0;
+}
+
+static void espi_claim_bus(struct fsl_spi *fsl)
+{
+	ccsr_espi_t *espi = fsl->espi;
+	uint32_t csmode;
+	int i;
+
+	/* Enable eSPI interface */
+	out_be32(&espi->mode, ESPI_MODE_RXTHR(3)
+			| ESPI_MODE_TXTHR(4) | ESPI_MODE_EN);
+
+	out_be32(&espi->mask, 0x00000000); /* Mask  all eSPI interrupts */
+
+	/* Init CS mode interface */
+	for (i = 0; i < ESPI_MAX_CS_NUM; i++)
+		out_be32(&espi->csmode[i], ESPI_CSMODE_INIT_VAL);
+
+	csmode = ESPI_CSMODE_INIT_VAL;
+
+	/* Set eSPI BRG clock source */
+	csmode |= ESPI_CSMODE_PM(fsl->pm) | fsl->div16;
+
+	/* Set eSPI mode */
+	if (fsl->mode & SPI_CPHA)
+		csmode |= ESPI_CSMODE_CP_BEGIN_EDGCLK;
+	if (fsl->mode & SPI_CPOL)
+		csmode |= ESPI_CSMODE_CI_INACTIVEHIGH;
+
+	/* Character bit order: msb first */
+	csmode |= ESPI_CSMODE_REV_MSB_FIRST;
+
+	/* Character length in bits, between 0x3~0xf, i.e. 4bits~16bits */
+	csmode |= ESPI_CSMODE_LEN(7);
+
+	out_be32(&espi->csmode[fsl->cs], csmode);
+}
+
+static void espi_release_bus(struct fsl_spi *fsl)
+{
+	/* Disable the SPI hardware */
+	out_be32(&fsl->espi->mode,
+		in_be32(&fsl->espi->mode) & (~ESPI_MODE_EN));
+}
+
+static void espi_setup_spi(struct fsl_spi *fsl, unsigned int max_hz)
+{
+	unsigned long spibrg;
+	uint32_t pm;
+
+	spibrg = CONFIG_FREQ_SYSTEMBUS / 2;
+	fsl->div16 = 0;
+	if ((spibrg / max_hz) > 32) {
+		fsl->div16 = ESPI_CSMODE_DIV16;
+		pm = spibrg / (max_hz * 16 * 2);
+		if (pm > 16) {
+			/* max_hz too low */
+			pm = 16;
+		}
+	} else {
+		pm = spibrg / (max_hz * 2);
+	}
+	if (pm)
+		pm--;
+	fsl->pm = pm;
+}
+
+static struct fsl_spi spi;
+
+int spi_init(unsigned int cs, unsigned int max_hz, unsigned int mode)
+{
+	if (cs >= ESPI_MAX_CS_NUM)
+		return -1;
+
+	spi.espi = (ccsr_espi_t *)CONFIG_SPI_FSL_ESPI_REG_BASE;
+	spi.cs = cs;
+	spi.mode = mode;
+
+	espi_setup_spi(&spi, max_hz);
+
+	return 0;
+}
+
+int spi_claim_bus(void)
+{
+	espi_claim_bus(&spi);
+
+	return 0;
+}
+
+void spi_release_bus(void)
+{
+	espi_release_bus(&spi);
+}
+
+int spi_xfer(const struct spi_transfer *msg, int n)
+{
+	return espi_xfer(&spi, msg, n);
+}
+
+size_t spi_max_xfer(void)
+{
+	return ESPI_MAX_DATA_TRANSFER_LEN;
+}

target/linux/mpc85xx/image/spi-loader/drivers/spi/spi-nor.c

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#include <spi.h>
+#include <spi-nor.h>
+#include <stdio.h>
+
+#define CMD_READ 0x03
+#define CMD_READ_ID 0x9F
+
+int spi_nor_read_id(void)
+{
+	int ret;
+
+	const uint8_t tx_buf[1] = {CMD_READ_ID};
+	uint8_t rx_buf[3] = {};
+	struct spi_transfer t[2] = {{
+		.tx_buf = tx_buf,
+		.rx_buf = NULL,
+		.len = sizeof(tx_buf),
+	}, {
+		.tx_buf = NULL,
+		.rx_buf = rx_buf,
+		.len = sizeof(rx_buf),
+	}};
+
+	ret = spi_xfer(t, ARRAY_SIZE(t));
+	if (ret) {
+		puts("SPI transfer failed\n");
+		return ret;
+	}
+
+	puts("Flash JECED ID: ");
+	put_array(rx_buf, sizeof(rx_buf));
+
+	return 0;
+}
+
+int spi_nor_read_data(void *dest, size_t pos, size_t len)
+{
+	int ret;
+
+	while (len > 0) {
+		uint8_t cmd[4] = {CMD_READ, pos >> 16, pos >> 8, pos};
+		size_t block_len = min(len, spi_max_xfer() - sizeof(cmd));
+
+		struct spi_transfer t[2] = {{
+			.tx_buf = cmd,
+			.rx_buf = NULL,
+			.len = sizeof(cmd),
+		}, {
+			.tx_buf = NULL,
+			.rx_buf = dest,
+			.len = block_len,
+		}};
+
+		ret = spi_xfer(t, ARRAY_SIZE(t));
+		if (ret) {
+			puts("SPI transfer failed\n");
+			return ret;
+		}
+
+		pos += block_len;
+		dest += block_len;
+		len -= block_len;
+	}
+
+	return 0;
+}
+

target/linux/mpc85xx/image/spi-loader/head.S

@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ *
+ * Based on Linux arch/powerpc/boot/crt0.S, which is:
+ *
+ * Copyright (C) Paul Mackerras 1997.
+ */
+
+#include <ppc_asm.h>
+
+	.text
+	.global _start
+_start:
+	/* Do a cache flush for our text, in case the loader didn't */
+	lis	r3,_text_start@ha
+	addi	r3,r3,_text_start@l
+	li	r4,_text_len
+	bl	flush_cache
+
+	/* Clear the BSS */
+	lis	r3,_bss_start@ha
+	addi	r3,r3,_bss_start@l
+	li	r4,0
+	li	r5,_bss_len
+	bl	memset
+
+	/* Set up stack */
+	lis	r1,_stack_top@ha
+	addi	r1,r1,_stack_top@l
+	/* Establish a stack frame */
+	li	r0,0
+	stwu	r0,-16(r1)
+
+	/* Call start */
+	b	start

target/linux/mpc85xx/image/spi-loader/include/image.h

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Derived from U-Boot include/image.h:
+ *
+ * (C) Copyright 2008 Semihalf
+ *
+ * (C) Copyright 2000-2005
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ ********************************************************************
+ * NOTE: This header file defines an interface to U-Boot. Including
+ * this (unmodified) header file in another file is considered normal
+ * use of U-Boot, and does *not* fall under the heading of "derived
+ * work".
+ ********************************************************************
+ */
+
+#pragma once
+
+#include <types.h>
+
+/*
+ * Compression Types
+ *
+ * The following are exposed to uImage header.
+ * New IDs *MUST* be appended at the end of the list and *NEVER*
+ * inserted for backward compatibility.
+ */
+enum {
+	IH_COMP_NONE		= 0,	/*  No	 Compression Used	*/
+	IH_COMP_GZIP,			/* gzip	 Compression Used	*/
+	IH_COMP_BZIP2,			/* bzip2 Compression Used	*/
+	IH_COMP_LZMA,			/* lzma  Compression Used	*/
+	IH_COMP_LZO,			/* lzo   Compression Used	*/
+	IH_COMP_LZ4,			/* lz4   Compression Used	*/
+	IH_COMP_ZSTD,			/* zstd   Compression Used	*/
+
+	IH_COMP_COUNT,
+};
+
+#define IH_MAGIC	0x27051956	/* Image Magic Number		*/
+#define IH_MAGIC_OKLI	0x4f4b4c49	/* 'OKLI' Magic Number */
+#define IH_NMLEN		32	/* Image Name Length		*/
+
+/*
+ * Legacy format image header,
+ * all data in network byte order (aka natural aka bigendian).
+ */
+typedef struct image_header {
+	uint32_t	ih_magic;	/* Image Header Magic Number	*/
+	uint32_t	ih_hcrc;	/* Image Header CRC Checksum	*/
+	uint32_t	ih_time;	/* Image Creation Timestamp	*/
+	uint32_t	ih_size;	/* Image Data Size		*/
+	uint32_t	ih_load;	/* Data	 Load  Address		*/
+	uint32_t	ih_ep;		/* Entry Point Address		*/
+	uint32_t	ih_dcrc;	/* Image Data CRC Checksum	*/
+	uint8_t		ih_os;		/* Operating System		*/
+	uint8_t		ih_arch;	/* CPU architecture		*/
+	uint8_t		ih_type;	/* Image Type			*/
+	uint8_t		ih_comp;	/* Compression Type		*/
+	uint8_t		ih_name[IH_NMLEN];	/* Image Name		*/
+} image_header_t;

target/linux/mpc85xx/image/spi-loader/include/init.h

@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#pragma once
+
+void start(void);

target/linux/mpc85xx/image/spi-loader/include/io.h

@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#pragma once
+
+#include <stdint.h>
+
+/*
+ * Low-level I/O routines.
+ *
+ * Copied from <file:arch/powerpc/include/asm/io.h> (which has no copyright)
+ */
+static inline uint8_t in_8(const volatile uint8_t *addr)
+{
+	int ret;
+
+	__asm__ __volatile__("lbz%U1%X1 %0,%1; twi 0,%0,0; isync"
+			     : "=r" (ret) : "m" (*addr));
+	return ret;
+}
+
+static inline void out_8(volatile uint8_t *addr, uint8_t val)
+{
+	__asm__ __volatile__("stb%U0%X0 %1,%0; sync"
+			     : "=m" (*addr) : "r" (val));
+}
+
+static inline uint16_t in_le16(const volatile uint16_t *addr)
+{
+	uint32_t ret;
+
+	__asm__ __volatile__("lhbrx %0,0,%1; twi 0,%0,0; isync"
+			     : "=r" (ret) : "r" (addr), "m" (*addr));
+
+	return ret;
+}
+
+static inline uint16_t in_be16(const volatile uint16_t *addr)
+{
+	uint32_t ret;
+
+	__asm__ __volatile__("lhz%U1%X1 %0,%1; twi 0,%0,0; isync"
+			     : "=r" (ret) : "m" (*addr));
+	return ret;
+}
+
+static inline void out_le16(volatile uint16_t *addr, uint16_t val)
+{
+	__asm__ __volatile__("sthbrx %1,0,%2; sync" : "=m" (*addr)
+			     : "r" (val), "r" (addr));
+}
+
+static inline void out_be16(volatile uint16_t *addr, uint16_t val)
+{
+	__asm__ __volatile__("sth%U0%X0 %1,%0; sync"
+			     : "=m" (*addr) : "r" (val));
+}
+
+static inline uint32_t in_le32(const volatile uint32_t *addr)
+{
+	uint32_t ret;
+
+	__asm__ __volatile__("lwbrx %0,0,%1; twi 0,%0,0; isync"
+			     : "=r" (ret) : "r" (addr), "m" (*addr));
+	return ret;
+}
+
+static inline uint32_t in_be32(const volatile uint32_t *addr)
+{
+	uint32_t ret;
+
+	__asm__ __volatile__("lwz%U1%X1 %0,%1; twi 0,%0,0; isync"
+			     : "=r" (ret) : "m" (*addr));
+	return ret;
+}
+
+static inline void out_le32(volatile uint32_t *addr, uint32_t val)
+{
+	__asm__ __volatile__("stwbrx %1,0,%2; sync" : "=m" (*addr)
+			     : "r" (val), "r" (addr));
+}
+
+static inline void out_be32(volatile uint32_t *addr, uint32_t val)
+{
+	__asm__ __volatile__("stw%U0%X0 %1,%0; sync"
+			     : "=m" (*addr) : "r" (val));
+}
+
+static inline void sync(void)
+{
+	asm volatile("sync" : : : "memory");
+}
+
+static inline void eieio(void)
+{
+	asm volatile("eieio" : : : "memory");
+}
+
+static inline void barrier(void)
+{
+	asm volatile("" : : : "memory");
+}

target/linux/mpc85xx/image/spi-loader/include/ppc_asm.h

@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#pragma once
+/*
+ *
+ * Definitions used by various bits of low-level assembly code on PowerPC.
+ *
+ * Copyright (C) 1995-1999 Gary Thomas, Paul Mackerras, Cort Dougan.
+ */
+
+/* Condition Register Bit Fields */
+
+#define	cr0	0
+#define	cr1	1
+#define	cr2	2
+#define	cr3	3
+#define	cr4	4
+#define	cr5	5
+#define	cr6	6
+#define	cr7	7
+
+/* General Purpose Registers (GPRs) */
+
+#define	r0	0
+#define	r1	1
+#define	r2	2
+#define	r3	3
+#define	r4	4
+#define	r5	5
+#define	r6	6
+#define	r7	7
+#define	r8	8
+#define	r9	9
+#define	r10	10
+#define	r11	11
+#define	r12	12
+#define	r13	13
+#define	r14	14
+#define	r15	15
+#define	r16	16
+#define	r17	17
+#define	r18	18
+#define	r19	19
+#define	r20	20
+#define	r21	21
+#define	r22	22
+#define	r23	23
+#define	r24	24
+#define	r25	25
+#define	r26	26
+#define	r27	27
+#define	r28	28
+#define	r29	29
+#define	r30	30
+#define	r31	31

target/linux/mpc85xx/image/spi-loader/include/serial.h

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+#pragma once
+
+int serial_console_getchar(void);
+int serial_console_tstc(void);
+void serial_console_putchar(char c);
+void serial_console_init(void);
+

target/linux/mpc85xx/image/spi-loader/include/spi-nor.h

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#pragma once
+
+#include <types.h>
+
+int spi_nor_read_id(void);
+int spi_nor_read_data(void *dest, size_t pos, size_t len);

target/linux/mpc85xx/image/spi-loader/include/spi.h

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Common SPI Interface: Controller-specific definitions
+ *
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ *
+ * Based on U-boot's spi.h:
+ *
+ * (C) Copyright 2001
+ * Gerald Van Baren, Custom IDEAS, vanbaren@cideas.com.
+ */
+
+#pragma once
+
+#include <types.h>
+
+/* SPI mode flags */
+#define SPI_CPHA	BIT(0)	/* clock phase (1 = SPI_CLOCK_PHASE_SECOND) */
+#define SPI_CPOL	BIT(1)	/* clock polarity (1 = SPI_POLARITY_HIGH) */
+#define SPI_MODE_0	(0|0)			/* (original MicroWire) */
+#define SPI_MODE_1	(0|SPI_CPHA)
+#define SPI_MODE_2	(SPI_CPOL|0)
+#define SPI_MODE_3	(SPI_CPOL|SPI_CPHA)
+
+struct spi_transfer {
+	const void *tx_buf;
+	void *rx_buf;
+	size_t len;
+};
+
+static inline size_t spi_message_len(const struct spi_transfer *msg, int n) {
+	size_t total = 0;
+	for (int i = 0; i < n; i++) {
+		total += msg[i].len;
+	}
+	return total;
+}
+
+int spi_init(unsigned int cs, unsigned int max_hz, unsigned int mode);
+int spi_claim_bus(void);
+void spi_release_bus(void);
+int spi_xfer(const struct spi_transfer *msg, int n);
+size_t spi_max_xfer(void);

target/linux/mpc85xx/image/spi-loader/include/stdio.h

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#pragma once
+
+#include <serial.h>
+#include <types.h>
+
+static inline int getchar(void)
+{
+	return serial_console_getchar();
+}
+
+static inline int tstc(void)
+{
+	return serial_console_tstc();
+}
+
+static inline int putchar(char c)
+{
+	if (c == '\n')
+		serial_console_putchar('\r');
+	serial_console_putchar(c);
+	return 0;
+}
+
+int puts(const char *s);
+
+/* Utility functions */
+void put_u4(uint8_t v);
+void put_u8(uint8_t v);
+void put_u16(uint16_t v);
+void put_u32(uint32_t v);
+void put_ptr(const void *p);
+void put_array(const void *p, size_t l);
+
+#define put_with_label(label, put, value) do { \
+		puts(label); \
+		put(value); \
+		puts("\n"); \
+	} while (0)

target/linux/mpc85xx/image/spi-loader/include/string.h

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#pragma once
+
+#include <stddef.h>
+
+extern char *strcpy(char *dest, const char *src);
+extern char *strncpy(char *dest, const char *src, size_t n);
+extern char *strcat(char *dest, const char *src);
+extern char *strchr(const char *s, int c);
+extern char *strrchr(const char *s, int c);
+extern int strcmp(const char *s1, const char *s2);
+extern int strncmp(const char *s1, const char *s2, size_t n);
+extern size_t strlen(const char *s);
+extern size_t strnlen(const char *s, size_t count);
+
+extern void *memset(void *s, int c, size_t n);
+extern void *memmove(void *dest, const void *src, unsigned long n);
+extern void *memcpy(void *dest, const void *src, unsigned long n);
+extern void *memchr(const void *s, int c, size_t n);
+extern int memcmp(const void *s1, const void *s2, size_t n);
+
+extern void flush_cache(void *, unsigned long);

target/linux/mpc85xx/image/spi-loader/include/types.h

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Code originates from Linux kernel arch/powerpc/boot
+ * (types.h, swab.h, of.h)
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+#define BIT(nr)	(1UL << (nr))
+
+#define min(x,y) ({ \
+	typeof(x) _x = (x);	\
+	typeof(y) _y = (y);	\
+	(void) (&_x == &_y);	\
+	_x < _y ? _x : _y; })
+
+#define max(x,y) ({ \
+	typeof(x) _x = (x);	\
+	typeof(y) _y = (y);	\
+	(void) (&_x == &_y);	\
+	_x > _y ? _x : _y; })
+
+#define min_t(type, a, b) min(((type) a), ((type) b))
+#define max_t(type, a, b) max(((type) a), ((type) b))
+
+static inline uint16_t swab16(uint16_t x)
+{
+	return  ((x & (uint16_t)0x00ffU) << 8) |
+		((x & (uint16_t)0xff00U) >> 8);
+}
+
+static inline uint32_t swab32(uint32_t x)
+{
+	return  ((x & (uint32_t)0x000000ffUL) << 24) |
+		((x & (uint32_t)0x0000ff00UL) <<  8) |
+		((x & (uint32_t)0x00ff0000UL) >>  8) |
+		((x & (uint32_t)0xff000000UL) >> 24);
+}
+
+static inline uint64_t swab64(uint64_t x)
+{
+	return  (uint64_t)((x & (uint64_t)0x00000000000000ffULL) << 56) |
+		(uint64_t)((x & (uint64_t)0x000000000000ff00ULL) << 40) |
+		(uint64_t)((x & (uint64_t)0x0000000000ff0000ULL) << 24) |
+		(uint64_t)((x & (uint64_t)0x00000000ff000000ULL) <<  8) |
+		(uint64_t)((x & (uint64_t)0x000000ff00000000ULL) >>  8) |
+		(uint64_t)((x & (uint64_t)0x0000ff0000000000ULL) >> 24) |
+		(uint64_t)((x & (uint64_t)0x00ff000000000000ULL) >> 40) |
+		(uint64_t)((x & (uint64_t)0xff00000000000000ULL) >> 56);
+}
+
+#ifdef __LITTLE_ENDIAN__
+#define cpu_to_be16(x) swab16(x)
+#define be16_to_cpu(x) swab16(x)
+#define cpu_to_be32(x) swab32(x)
+#define be32_to_cpu(x) swab32(x)
+#define cpu_to_be64(x) swab64(x)
+#define be64_to_cpu(x) swab64(x)
+#else
+#define cpu_to_be16(x) (x)
+#define be16_to_cpu(x) (x)
+#define cpu_to_be32(x) (x)
+#define be32_to_cpu(x) (x)
+#define cpu_to_be64(x) (x)
+#define be64_to_cpu(x) (x)
+#endif

target/linux/mpc85xx/image/spi-loader/loader.c

@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#include <image.h>
+#include <init.h>
+#include <spi.h>
+#include <spi-nor.h>
+#include <stdio.h>
+#include <string.h>
+
+static bool check_image_header(const image_header_t *header)
+{
+	if (header->ih_magic != cpu_to_be32(IH_MAGIC_OKLI)) {
+		puts("Invalid image magic\n");
+		return false;
+	}
+
+	if (header->ih_comp != cpu_to_be32(IH_COMP_NONE)) {
+		puts("Unsupported compressed image\n");
+		return false;
+	}
+
+	return true;
+}
+
+static uint32_t do_load(void)
+{
+	image_header_t header;
+	uint32_t ih_size, ih_load, ih_ep;
+
+	if (spi_nor_read_id())
+		return UINT32_MAX;
+
+	puts("Reading image header...\n");
+	if (spi_nor_read_data(&header, CONFIG_IMAGE_OFFSET, sizeof(header)))
+		return UINT32_MAX;
+
+	if (!check_image_header(&header))
+		return UINT32_MAX;
+
+	header.ih_name[sizeof(header.ih_name) - 1] = 0;
+	ih_size = be32_to_cpu(header.ih_size);
+	ih_load = be32_to_cpu(header.ih_load);
+	ih_ep = be32_to_cpu(header.ih_ep);
+
+	put_with_label("Image Name:   ", puts, (const char *)header.ih_name);
+	put_with_label("Data Size:    ", put_u32, ih_size);
+	put_with_label("Load Address: ", put_u32, ih_load);
+	put_with_label("Entry Point:  ", put_u32, ih_ep);
+
+	puts("Reading image data...\n");
+	void *loadaddr = (void *)ih_load;
+	if (spi_nor_read_data(loadaddr, CONFIG_IMAGE_OFFSET + sizeof(header),
+			      ih_size))
+		return false;
+
+	flush_cache(loadaddr, ih_size);
+
+	return ih_ep;
+}
+
+static void enter_image(uint32_t addr)
+{
+	typedef void (*entry_t)(void);
+	entry_t entry = (entry_t)addr;
+
+	puts("Starting image...\n");
+	entry();
+}
+
+static void load(void)
+{
+	uint32_t addr;
+	int ret;
+
+	ret = spi_init(0, CONFIG_SPI_MAX_HZ, SPI_MODE_0);
+	if (ret) {
+		puts("Failed to initialize SPI controller\n");
+		return;
+	}
+
+	ret = spi_claim_bus();
+	if (ret) {
+		puts("Failed to enable SPI controller\n");
+		return;
+	}
+
+	addr = do_load();
+
+	spi_release_bus();
+
+	if (addr != UINT32_MAX)
+		enter_image(addr);
+}
+
+void start(void)
+{
+	serial_console_init();
+	puts("=== " CONFIG_PROGRAM_NAME " ===\n");
+
+	load();
+
+	puts("Halting execution.\n");
+	while (true) {}
+}

target/linux/mpc85xx/image/spi-loader/loader.lds

@@ -0,0 +1,31 @@
+OUTPUT_ARCH(powerpc:common)
+ENTRY(_start)
+EXTERN(_start)
+SECTIONS {
+	.text :
+	{
+		_text_start = .;
+		*(.text*)
+		_text_len = ABSOLUTE(. - _text_start);
+	}
+	.data :
+	{
+		_data_start = .;
+		*(.rodata*)
+		*(.data*)
+		*(.sdata*)
+		_data_len = ABSOLUTE(. - _data_start);
+	}
+	. = ALIGN(4096);
+	.bss :
+	{
+		_bss_start = .;
+		. += 4K;
+		_stack_top = .;
+		*(.bss*)
+		*(.sbss*)
+		_bss_len = ABSOLUTE(. - _bss_start);
+	}
+	. = ALIGN(4096);
+	_end = .;
+}

target/linux/mpc85xx/image/spi-loader/stdio.c

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#include <stdio.h>
+
+int puts(const char *s)
+{
+	while (*s)
+		putchar(*s++);
+	return 0;
+}
+
+void put_u4(uint8_t v)
+{
+	v &= 0xf;
+	switch (v) {
+	case 0x0 ... 0x9:
+		putchar('0' + v);
+		break;
+	case 0xa ... 0xf:
+		putchar('a' + (v - 0xa));
+	}
+}
+
+void put_u8(uint8_t v)
+{
+	put_u4(v >> 4);
+	put_u4(v);
+}
+
+void put_u16(uint16_t v)
+{
+	put_u8(v >> 8);
+	put_u8(v);
+}
+
+void put_u32(uint32_t v)
+{
+	put_u16(v >> 16);
+	put_u16(v);
+}
+
+void put_ptr(const void *p)
+{
+	put_u32((uint32_t)p);
+}
+
+void put_array(const void *p, size_t l)
+{
+	const uint8_t *c = p;
+	size_t i;
+	for (i = 0; i < l; i++) {
+		put_u8(c[i]);
+		putchar(' ');
+	}
+	putchar('\n');
+}

target/linux/mpc85xx/image/spi-loader/string.S

@@ -0,0 +1,265 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) Paul Mackerras 1997.
+ *
+ * NOTE: this code runs in 32 bit mode and is packaged as ELF32.
+ */
+
+#include <ppc_asm.h>
+
+	.text
+	.globl	strcpy
+strcpy:
+	addi	r5,r3,-1
+	addi	r4,r4,-1
+1:	lbzu	r0,1(r4)
+	cmpwi	0,r0,0
+	stbu	r0,1(r5)
+	bne	1b
+	blr
+
+	.globl	strncpy
+strncpy:
+	cmpwi	0,r5,0
+	beqlr
+	mtctr	r5
+	addi	r6,r3,-1
+	addi	r4,r4,-1
+1:	lbzu	r0,1(r4)
+	cmpwi	0,r0,0
+	stbu	r0,1(r6)
+	bdnzf	2,1b		/* dec ctr, branch if ctr != 0 && !cr0.eq */
+	blr
+
+	.globl	strcat
+strcat:
+	addi	r5,r3,-1
+	addi	r4,r4,-1
+1:	lbzu	r0,1(r5)
+	cmpwi	0,r0,0
+	bne	1b
+	addi	r5,r5,-1
+1:	lbzu	r0,1(r4)
+	cmpwi	0,r0,0
+	stbu	r0,1(r5)
+	bne	1b
+	blr
+
+	.globl	strchr
+strchr:
+	addi	r3,r3,-1
+1:	lbzu	r0,1(r3)
+	cmpw	0,r0,r4
+	beqlr
+	cmpwi	0,r0,0
+	bne	1b
+	li	r3,0
+	blr
+
+	.globl	strcmp
+strcmp:
+	addi	r5,r3,-1
+	addi	r4,r4,-1
+1:	lbzu	r3,1(r5)
+	cmpwi	1,r3,0
+	lbzu	r0,1(r4)
+	subf.	r3,r0,r3
+	beqlr	1
+	beq	1b
+	blr
+
+	.globl	strncmp
+strncmp:
+	mtctr	r5
+	addi	r5,r3,-1
+	addi	r4,r4,-1
+1:	lbzu	r3,1(r5)
+	cmpwi	1,r3,0
+	lbzu	r0,1(r4)
+	subf.	r3,r0,r3
+	beqlr	1
+	bdnzt	eq,1b
+	blr
+
+	.globl	strlen
+strlen:
+	addi	r4,r3,-1
+1:	lbzu	r0,1(r4)
+	cmpwi	0,r0,0
+	bne	1b
+	subf	r3,r3,r4
+	blr
+
+	.globl	memset
+memset:
+	rlwimi	r4,r4,8,16,23
+	rlwimi	r4,r4,16,0,15
+	addi	r6,r3,-4
+	cmplwi	0,r5,4
+	blt	7f
+	stwu	r4,4(r6)
+	beqlr
+	andi.	r0,r6,3
+	add	r5,r0,r5
+	subf	r6,r0,r6
+	rlwinm	r0,r5,32-2,2,31
+	mtctr	r0
+	bdz	6f
+1:	stwu	r4,4(r6)
+	bdnz	1b
+6:	andi.	r5,r5,3
+7:	cmpwi	0,r5,0
+	beqlr
+	mtctr	r5
+	addi	r6,r6,3
+8:	stbu	r4,1(r6)
+	bdnz	8b
+	blr
+
+	.globl	memmove
+memmove:
+	cmplw	0,r3,r4
+	bgt	backwards_memcpy
+	/* fall through */
+
+	.globl	memcpy
+memcpy:
+	rlwinm.	r7,r5,32-3,3,31		/* r7 = r5 >> 3 */
+	addi	r6,r3,-4
+	addi	r4,r4,-4
+	beq	3f			/* if less than 8 bytes to do */
+	andi.	r0,r6,3			/* get dest word aligned */
+	mtctr	r7
+	bne	5f
+	andi.	r0,r4,3			/* check src word aligned too */
+	bne	3f
+1:	lwz	r7,4(r4)
+	lwzu	r8,8(r4)
+	stw	r7,4(r6)
+	stwu	r8,8(r6)
+	bdnz	1b
+	andi.	r5,r5,7
+2:	cmplwi	0,r5,4
+	blt	3f
+	lwzu	r0,4(r4)
+	addi	r5,r5,-4
+	stwu	r0,4(r6)
+3:	cmpwi	0,r5,0
+	beqlr
+	mtctr	r5
+	addi	r4,r4,3
+	addi	r6,r6,3
+4:	lbzu	r0,1(r4)
+	stbu	r0,1(r6)
+	bdnz	4b
+	blr
+5:	subfic	r0,r0,4
+	cmpw	cr1,r0,r5
+	add	r7,r0,r4
+	andi.	r7,r7,3			/* will source be word-aligned too? */
+	ble	cr1,3b
+	bne	3b			/* do byte-by-byte if not */
+	mtctr	r0
+6:	lbz	r7,4(r4)
+	addi	r4,r4,1
+	stb	r7,4(r6)
+	addi	r6,r6,1
+	bdnz	6b
+	subf	r5,r0,r5
+	rlwinm.	r7,r5,32-3,3,31
+	beq	2b
+	mtctr	r7
+	b	1b
+
+	.globl	backwards_memcpy
+backwards_memcpy:
+	rlwinm.	r7,r5,32-3,3,31		/* r7 = r5 >> 3 */
+	add	r6,r3,r5
+	add	r4,r4,r5
+	beq	3f
+	andi.	r0,r6,3
+	mtctr	r7
+	bne	5f
+	andi.	r0,r4,3
+	bne	3f
+1:	lwz	r7,-4(r4)
+	lwzu	r8,-8(r4)
+	stw	r7,-4(r6)
+	stwu	r8,-8(r6)
+	bdnz	1b
+	andi.	r5,r5,7
+2:	cmplwi	0,r5,4
+	blt	3f
+	lwzu	r0,-4(r4)
+	subi	r5,r5,4
+	stwu	r0,-4(r6)
+3:	cmpwi	0,r5,0
+	beqlr
+	mtctr	r5
+4:	lbzu	r0,-1(r4)
+	stbu	r0,-1(r6)
+	bdnz	4b
+	blr
+5:	cmpw	cr1,r0,r5
+	subf	r7,r0,r4
+	andi.	r7,r7,3
+	ble	cr1,3b
+	bne	3b
+	mtctr	r0
+6:	lbzu	r7,-1(r4)
+	stbu	r7,-1(r6)
+	bdnz	6b
+	subf	r5,r0,r5
+	rlwinm.	r7,r5,32-3,3,31
+	beq	2b
+	mtctr	r7
+	b	1b
+
+	.globl	memchr
+memchr:
+	cmpwi	0,r5,0
+	blelr
+	mtctr	r5
+	addi	r3,r3,-1
+1:	lbzu	r0,1(r3)
+	cmpw	r0,r4
+	beqlr
+	bdnz	1b
+	li	r3,0
+	blr
+
+	.globl	memcmp
+memcmp:
+	cmpwi	0,r5,0
+	ble	2f
+	mtctr	r5
+	addi	r6,r3,-1
+	addi	r4,r4,-1
+1:	lbzu	r3,1(r6)
+	lbzu	r0,1(r4)
+	subf.	r3,r0,r3
+	bdnzt	2,1b
+	blr
+2:	li	r3,0
+	blr
+
+
+/*
+ * Flush the dcache and invalidate the icache for a range of addresses.
+ *
+ * flush_cache(addr, len)
+ */
+	.global	flush_cache
+flush_cache:
+	addi	4,4,0x1f	/* len = (len + 0x1f) / 0x20 */
+	rlwinm.	4,4,27,5,31
+	mtctr	4
+	beqlr
+1:	dcbf	0,3
+	icbi	0,3
+	addi	3,3,0x20
+	bdnz	1b
+	sync
+	isync
+	blr
+