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/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) {}
+}