block: add support for partition table defined in OF

Add support for partition table defined in Device Tree. Similar to how
it's done with MTD, add support for defining a fixed partition table in
device tree.

A common scenario for this is fixed block (eMMC) embedded devices that
have no MBR or GPT partition table to save storage space. Bootloader
access the block device with absolute address of data.

This is to complete the functionality with an equivalent implementation
with providing partition table with bootargs, for case where the booargs
can't be modified and tweaking the Device Tree is the only solution to
have an usabe partition table.

The implementation follow the fixed-partitions parser used on MTD
devices where a "partitions" node is expected to be declared with
"fixed-partitions" compatible in the OF node of the disk device
(mmc-card for eMMC for example) and each child node declare a label
and a reg with offset and size. If label is not declared, the node name
is used as fallback. Eventually is also possible to declare the read-only
property to flag the partition as read-only.

Signed-off-by: Christian Marangi <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

block/partitions/Kconfig

···
 	  Say Y here if you want to read the partition table from bootargs.
 	  The format for the command line is just like mtdparts.
 
+config OF_PARTITION
+	bool "Device Tree partition support" if PARTITION_ADVANCED
+	depends on OF
+	help
+	  Say Y here if you want to enable support for partition table
+	  defined in Device Tree. (mainly for eMMC)
+	  The format for the device tree node is just like MTD fixed-partition
+	  schema.
+
 endmenu

block/partitions/Makefile

···
 obj-$(CONFIG_MAC_PARTITION) += mac.o
 obj-$(CONFIG_LDM_PARTITION) += ldm.o
 obj-$(CONFIG_MSDOS_PARTITION) += msdos.o
+obj-$(CONFIG_OF_PARTITION) += of.o
 obj-$(CONFIG_OSF_PARTITION) += osf.o
 obj-$(CONFIG_SGI_PARTITION) += sgi.o
 obj-$(CONFIG_SUN_PARTITION) += sun.o

block/partitions/check.h

···
 int ldm_partition(struct parsed_partitions *state);
 int mac_partition(struct parsed_partitions *state);
 int msdos_partition(struct parsed_partitions *state);
+int of_partition(struct parsed_partitions *state);
 int osf_partition(struct parsed_partitions *state);
 int sgi_partition(struct parsed_partitions *state);
 int sun_partition(struct parsed_partitions *state);

block/partitions/core.c

···
 #ifdef CONFIG_CMDLINE_PARTITION
 	cmdline_partition,
 #endif
+#ifdef CONFIG_OF_PARTITION
+	of_partition,		/* cmdline have priority to OF */
+#endif
 #ifdef CONFIG_EFI_PARTITION
 	efi_partition,		/* this must come before msdos */
 #endif

block/partitions/of.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/blkdev.h>
+#include <linux/major.h>
+#include <linux/of.h>
+#include <linux/string.h>
+#include "check.h"
+
+static int validate_of_partition(struct device_node *np, int slot)
+{
+	u64 offset, size;
+	int len;
+
+	const __be32 *reg = of_get_property(np, "reg", &len);
+	int a_cells = of_n_addr_cells(np);
+	int s_cells = of_n_size_cells(np);
+
+	/* Make sure reg len match the expected addr and size cells */
+	if (len / sizeof(*reg) != a_cells + s_cells)
+		return -EINVAL;
+
+	/* Validate offset conversion from bytes to sectors */
+	offset = of_read_number(reg, a_cells);
+	if (offset % SECTOR_SIZE)
+		return -EINVAL;
+
+	/* Validate size conversion from bytes to sectors */
+	size = of_read_number(reg + a_cells, s_cells);
+	if (!size || size % SECTOR_SIZE)
+		return -EINVAL;
+
+	return 0;
+}
+
+static void add_of_partition(struct parsed_partitions *state, int slot,
+			     struct device_node *np)
+{
+	struct partition_meta_info *info;
+	char tmp[sizeof(info->volname) + 4];
+	const char *partname;
+	int len;
+
+	const __be32 *reg = of_get_property(np, "reg", &len);
+	int a_cells = of_n_addr_cells(np);
+	int s_cells = of_n_size_cells(np);
+
+	/* Convert bytes to sector size */
+	u64 offset = of_read_number(reg, a_cells) / SECTOR_SIZE;
+	u64 size = of_read_number(reg + a_cells, s_cells) / SECTOR_SIZE;
+
+	put_partition(state, slot, offset, size);
+
+	if (of_property_read_bool(np, "read-only"))
+		state->parts[slot].flags |= ADDPART_FLAG_READONLY;
+
+	/*
+	 * Follow MTD label logic, search for label property,
+	 * fallback to node name if not found.
+	 */
+	info = &state->parts[slot].info;
+	partname = of_get_property(np, "label", &len);
+	if (!partname)
+		partname = of_get_property(np, "name", &len);
+	strscpy(info->volname, partname, sizeof(info->volname));
+
+	snprintf(tmp, sizeof(tmp), "(%s)", info->volname);
+	strlcat(state->pp_buf, tmp, PAGE_SIZE);
+}
+
+int of_partition(struct parsed_partitions *state)
+{
+	struct device *ddev = disk_to_dev(state->disk);
+	struct device_node *np;
+	int slot;
+
+	struct device_node *partitions_np = of_node_get(ddev->of_node);
+
+	if (!partitions_np ||
+	    !of_device_is_compatible(partitions_np, "fixed-partitions"))
+		return 0;
+
+	slot = 1;
+	/* Validate parition offset and size */
+	for_each_child_of_node(partitions_np, np) {
+		if (validate_of_partition(np, slot)) {
+			of_node_put(np);
+			of_node_put(partitions_np);
+
+			return -1;
+		}
+
+		slot++;
+	}
+
+	slot = 1;
+	for_each_child_of_node(partitions_np, np) {
+		if (slot >= state->limit) {
+			of_node_put(np);
+			break;
+		}
+
+		add_of_partition(state, slot, np);
+
+		slot++;
+	}
+
+	strlcat(state->pp_buf, "\n", PAGE_SIZE);
+
+	return 1;
+}