[RFC PATCH 6/6] block: implement NVMEM provider

[Daniel Golle]

On embedded devices using an eMMC it is common that one or more partitions
on the eMMC are used to store MAC addresses and Wi-Fi calibration EEPROM
data. Allow referencing the partition in device tree for the kernel and
Wi-Fi drivers accessing it via the NVMEM layer.

Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
---
 block/Kconfig           |   8 ++
 block/Makefile          |   1 +
 block/blk-nvmem.c       | 187 ++++++++++++++++++++++++++++++++++++++++
 block/blk.h             |  13 +++
 block/genhd.c           |   2 +
 block/partitions/core.c |   2 +
 6 files changed, 213 insertions(+)
 create mode 100644 block/blk-nvmem.c

diff --git a/block/Kconfig b/block/Kconfig
index 86122e459fe04..185573877964d 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -218,6 +218,14 @@ config BLK_MQ_VIRTIO
 config BLK_PM
 	def_bool PM
 
+config BLK_NVMEM
+	bool "Block device NVMEM provider"
+	depends on OF
+	help
+	  Allow block devices (or partitions) to act as NVMEM prodivers,
+	  typically using if an eMMC is used to store MAC addresses or Wi-Fi
+	  calibration data on embedded devices.
+
 # do not use in new code
 config BLOCK_HOLDER_DEPRECATED
 	bool
diff --git a/block/Makefile b/block/Makefile
index 46ada9dc8bbfe..03c0bfa8642df 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_BLK_DEV_ZONED)	+= blk-zoned.o
 obj-$(CONFIG_BLK_WBT)		+= blk-wbt.o
 obj-$(CONFIG_BLK_DEBUG_FS)	+= blk-mq-debugfs.o
 obj-$(CONFIG_BLK_DEBUG_FS_ZONED)+= blk-mq-debugfs-zoned.o
+obj-$(CONFIG_BLK_NVMEM)		+= blk-nvmem.o
 obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
 obj-$(CONFIG_BLK_PM)		+= blk-pm.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= blk-crypto.o blk-crypto-profile.o \
diff --git a/block/blk-nvmem.c b/block/blk-nvmem.c
new file mode 100644
index 0000000000000..8238511049f56
--- /dev/null
+++ b/block/blk-nvmem.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * block device NVMEM provider
+ *
+ * Copyright (c) 2023 Daniel Golle <daniel@xxxxxxxxxxxxxx>
+ *
+ * Useful on devices using a partition on an eMMC for MAC addresses or
+ * Wi-Fi calibration EEPROM data.
+ */
+
+#include "blk.h"
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+#include <linux/pagemap.h>
+#include <linux/property.h>
+
+/* List of all NVMEM devices */
+static LIST_HEAD(nvmem_devices);
+static DEFINE_MUTEX(devices_mutex);
+
+struct blk_nvmem {
+	struct nvmem_device *nvmem;
+	struct block_device *bdev;
+	struct list_head list;
+};
+
+static int blk_nvmem_reg_read(void *priv, unsigned int from,
+			      void *val, size_t bytes)
+{
+	pgoff_t f_index = from >> PAGE_SHIFT;
+	struct address_space *mapping;
+	struct blk_nvmem *bnv = priv;
+	size_t bytes_left = bytes;
+	struct folio *folio;
+	unsigned long offs, to_read;
+	void *p;
+
+	if (!bnv->bdev)
+		return -ENODEV;
+
+	offs = from & ((1 << PAGE_SHIFT) - 1);
+	mapping = bnv->bdev->bd_inode->i_mapping;
+
+	while (bytes_left) {
+		folio = read_mapping_folio(mapping, f_index++, NULL);
+		if (IS_ERR(folio))
+			return PTR_ERR(folio);
+
+		to_read = min_t(unsigned long, bytes_left, PAGE_SIZE - offs);
+		p = folio_address(folio) + offset_in_folio(folio, offs);
+		memcpy(val, p, to_read);
+		offs = 0;
+		bytes_left -= to_read;
+		val += to_read;
+		folio_put(folio);
+	}
+
+	return bytes_left == 0 ? 0 : -EIO;
+}
+
+void blk_register_nvmem(struct block_device *bdev)
+{
+	struct fwnode_handle *fw_parts = NULL, *fw_part_c, *fw_part = NULL;
+	struct nvmem_config config = {};
+	const char *partname, *uuid;
+	struct device *dev, *p0dev;
+	struct blk_nvmem *bnv;
+	u32 reg;
+
+	/*
+	 * skip devices which set GENHD_FL_NO_NVMEM
+	 *
+	 * This flag is used for mtdblock and ubiblock devices because
+	 * both, MTD and UBI already implement their own NVMEM provider.
+	 * To avoid registering multiple NVMEM providers for the same
+	 * device node, skip the block NVMEM provider.
+	 */
+	if (bdev->bd_disk->flags & GENHD_FL_NO_NVMEM)
+		return;
+
+	/* skip too large devices */
+	if (bdev_nr_bytes(bdev) > INT_MAX)
+		return;
+
+	dev = &bdev->bd_device;
+	if (!bdev_is_partition(bdev)) {
+		fw_part = dev->fwnode;
+
+		if (!fw_part && dev->parent)
+			fw_part = dev->parent->fwnode;
+
+		goto no_parts;
+	}
+
+	p0dev = &bdev->bd_disk->part0->bd_device;
+	fw_parts = device_get_named_child_node(p0dev, "partitions");
+	if (!fw_parts)
+		fw_parts = device_get_named_child_node(p0dev->parent, "partitions");
+
+	if (!fw_parts)
+		return;
+
+	fwnode_for_each_child_node(fw_parts, fw_part_c) {
+		if (!fwnode_property_read_string(fw_part_c, "uuid", &uuid) &&
+		    (!bdev->bd_meta_info || strncmp(uuid,
+						    bdev->bd_meta_info->uuid,
+						    PARTITION_META_INFO_UUIDLTH)))
+			continue;
+
+		if (!fwnode_property_read_string(fw_part_c, "partname", &partname) &&
+		    (!bdev->bd_meta_info || strncmp(partname,
+						    bdev->bd_meta_info->volname,
+						    PARTITION_META_INFO_VOLNAMELTH)))
+			continue;
+
+		/*
+		 * partition addresses (reg) in device tree greater than
+		 * DISK_MAX_PARTS can be used to match uuid or partname only
+		 */
+		if (!fwnode_property_read_u32(fw_part_c, "reg", &reg) &&
+		    reg < DISK_MAX_PARTS && bdev->bd_partno != reg)
+			continue;
+
+		fw_part = fw_part_c;
+		break;
+	}
+
+no_parts:
+	if (!fwnode_device_is_compatible(fw_part, "nvmem-cells"))
+		return;
+
+	bnv = kzalloc(sizeof(struct blk_nvmem), GFP_KERNEL);
+	if (!bnv)
+		return;
+
+	config.id = NVMEM_DEVID_NONE;
+	config.dev = &bdev->bd_device;
+	config.name = dev_name(&bdev->bd_device);
+	config.owner = THIS_MODULE;
+	config.priv = bnv;
+	config.reg_read = blk_nvmem_reg_read;
+	config.size = bdev_nr_bytes(bdev);
+	config.word_size = 1;
+	config.stride = 1;
+	config.read_only = true;
+	config.root_only = true;
+	config.ignore_wp = true;
+	config.of_node = to_of_node(fw_part);
+
+	bnv->bdev = bdev;
+	bnv->nvmem = nvmem_register(&config);
+	if (IS_ERR(bnv->nvmem)) {
+		/* Just ignore if there is no NVMEM support in the kernel */
+		if (PTR_ERR(bnv->nvmem) != -EOPNOTSUPP)
+			dev_err_probe(&bdev->bd_device, PTR_ERR(bnv->nvmem),
+				      "Failed to register NVMEM device\n");
+
+		kfree(bnv);
+		return;
+	}
+
+	mutex_lock(&devices_mutex);
+	list_add_tail(&bnv->list, &nvmem_devices);
+	mutex_unlock(&devices_mutex);
+}
+
+void blk_unregister_nvmem(struct block_device *bdev)
+{
+	struct blk_nvmem *bnv_c, *bnv = NULL;
+
+	mutex_lock(&devices_mutex);
+	list_for_each_entry(bnv_c, &nvmem_devices, list)
+		if (bnv_c->bdev == bdev) {
+			bnv = bnv_c;
+			break;
+		}
+
+	if (!bnv) {
+		mutex_unlock(&devices_mutex);
+		return;
+	}
+
+	list_del(&bnv->list);
+	mutex_unlock(&devices_mutex);
+	nvmem_unregister(bnv->nvmem);
+	kfree(bnv);
+}
diff --git a/block/blk.h b/block/blk.h
index 686712e138352..7423d0d5494e9 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -515,4 +515,17 @@ static inline int req_ref_read(struct request *req)
 	return atomic_read(&req->ref);
 }
 
+#ifdef CONFIG_BLK_NVMEM
+void blk_register_nvmem(struct block_device *bdev);
+void blk_unregister_nvmem(struct block_device *bdev);
+#else
+static inline void blk_register_nvmem(struct block_device *bdev)
+{
+}
+
+static inline void blk_unregister_nvmem(struct block_device *bdev)
+{
+}
+#endif
+
 #endif /* BLK_INTERNAL_H */
diff --git a/block/genhd.c b/block/genhd.c
index 3d287b32d50df..b306e0f407bb2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -527,6 +527,7 @@ int __must_check device_add_disk(struct device *parent, struct gendisk *disk,
 	disk_update_readahead(disk);
 	disk_add_events(disk);
 	set_bit(GD_ADDED, &disk->state);
+	blk_register_nvmem(disk->part0);
 	return 0;
 
 out_unregister_bdi:
@@ -569,6 +570,7 @@ static void blk_report_disk_dead(struct gendisk *disk)
 		if (bdev->bd_holder_ops && bdev->bd_holder_ops->mark_dead)
 			bdev->bd_holder_ops->mark_dead(bdev);
 		mutex_unlock(&bdev->bd_holder_lock);
+		blk_unregister_nvmem(bdev);
 
 		put_device(&bdev->bd_device);
 		rcu_read_lock();
diff --git a/block/partitions/core.c b/block/partitions/core.c
index 13a7341299a91..68bd655f5e68e 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -404,6 +404,8 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	/* suppress uevent if the disk suppresses it */
 	if (!dev_get_uevent_suppress(ddev))
 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
+
+	blk_register_nvmem(bdev);
 	return bdev;
 
 out_del:
-- 
2.41.0