mtd: parsers: add Broadcom's U-Boot parser

Broadcom stores environment variables blocks inside U-Boot partition
itself. This driver finds & registers them.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220711153041.6036-2-zajec5@gmail.com

drivers/mtd/parsers/Kconfig

@@ -20,6 +20,16 @@ config MTD_BCM63XX_PARTS
 	  This provides partition parsing for BCM63xx devices with CFE
 	  bootloaders.
 
+config MTD_BRCM_U_BOOT
+	tristate "Broadcom's U-Boot partition parser"
+	depends on ARCH_BCM4908 || COMPILE_TEST
+	help
+	  Broadcom uses a custom way of storing U-Boot environment variables.
+	  They are placed inside U-Boot partition itself at unspecified offset.
+	  It's possible to locate them by looking for a custom header with a
+	  magic value. This driver does that and creates subpartitions for
+	  each found environment variables block.
+
 config MTD_CMDLINE_PARTS
 	tristate "Command line partition table parsing"
 	depends on MTD

drivers/mtd/parsers/Makefile

@@ -2,6 +2,7 @@
 obj-$(CONFIG_MTD_AR7_PARTS)		+= ar7part.o
 obj-$(CONFIG_MTD_BCM47XX_PARTS)		+= bcm47xxpart.o
 obj-$(CONFIG_MTD_BCM63XX_PARTS)		+= bcm63xxpart.o
+obj-$(CONFIG_MTD_BRCM_U_BOOT)		+= brcm_u-boot.o
 obj-$(CONFIG_MTD_CMDLINE_PARTS)		+= cmdlinepart.o
 obj-$(CONFIG_MTD_OF_PARTS)		+= ofpart.o
 ofpart-y				+= ofpart_core.o

drivers/mtd/parsers/brcm_u-boot.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright © 2022 Rafał Miłecki <rafal@milecki.pl>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/partitions.h>
+
+#define BRCM_U_BOOT_MAX_OFFSET		0x200000
+#define BRCM_U_BOOT_STEP		0x1000
+
+#define BRCM_U_BOOT_MAX_PARTS		2
+
+#define BRCM_U_BOOT_MAGIC		0x75456e76	/* uEnv */
+
+struct brcm_u_boot_header {
+	__le32 magic;
+	__le32 length;
+} __packed;
+
+static const char *names[BRCM_U_BOOT_MAX_PARTS] = {
+	"u-boot-env",
+	"u-boot-env-backup",
+};
+
+static int brcm_u_boot_parse(struct mtd_info *mtd,
+			     const struct mtd_partition **pparts,
+			     struct mtd_part_parser_data *data)
+{
+	struct brcm_u_boot_header header;
+	struct mtd_partition *parts;
+	size_t bytes_read;
+	size_t offset;
+	int err;
+	int i = 0;
+
+	parts = kcalloc(BRCM_U_BOOT_MAX_PARTS, sizeof(*parts), GFP_KERNEL);
+	if (!parts)
+		return -ENOMEM;
+
+	for (offset = 0;
+	     offset < min_t(size_t, mtd->size, BRCM_U_BOOT_MAX_OFFSET);
+	     offset += BRCM_U_BOOT_STEP) {
+		err = mtd_read(mtd, offset, sizeof(header), &bytes_read, (uint8_t *)&header);
+		if (err && !mtd_is_bitflip(err)) {
+			pr_err("Failed to read from %s at 0x%zx: %d\n", mtd->name, offset, err);
+			continue;
+		}
+
+		if (le32_to_cpu(header.magic) != BRCM_U_BOOT_MAGIC)
+			continue;
+
+		parts[i].name = names[i];
+		parts[i].offset = offset;
+		parts[i].size = sizeof(header) + le32_to_cpu(header.length);
+		i++;
+		pr_info("offset:0x%zx magic:0x%08x BINGO\n", offset, header.magic);
+
+		if (i == BRCM_U_BOOT_MAX_PARTS)
+			break;
+	}
+
+	*pparts = parts;
+
+	return i;
+};
+
+static const struct of_device_id brcm_u_boot_of_match_table[] = {
+	{ .compatible = "brcm,u-boot" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, brcm_u_boot_of_match_table);
+
+static struct mtd_part_parser brcm_u_boot_mtd_parser = {
+	.parse_fn = brcm_u_boot_parse,
+	.name = "brcm_u-boot",
+	.of_match_table = brcm_u_boot_of_match_table,
+};
+module_mtd_part_parser(brcm_u_boot_mtd_parser);
+
+MODULE_LICENSE("GPL");