[PATCH v7 5/9] block: implement NVMEM provider

[Loic Poulain <loic.poulain@oss.qualcomm.com>]

From: Daniel Golle <daniel@makrotopia.org>

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.

NVMEM is registered for a block device whose OF node describes an NVMEM
layout, either via an "nvmem-layout" child or by being a "fixed-layout"
node itself (e.g. an eMMC boot partition associated through its mmc-card
node).

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Co-developed-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
 block/Kconfig             |   9 ++++
 block/Makefile            |   1 +
 block/blk-nvmem.c         | 109 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk.h               |   8 ++++
 block/genhd.c             |   4 ++
 include/linux/blk_types.h |   4 ++
 6 files changed, 135 insertions(+)

diff --git a/block/Kconfig b/block/Kconfig
index 15027963472d7b40e27b9097a5993c457b5b3054..0b33747e16dc33473683706f75c92bdf8b648f7c 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -209,6 +209,15 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
 	  by falling back to the kernel crypto API when inline
 	  encryption hardware is not present.
 
+config BLK_NVMEM
+	bool "Block device NVMEM provider"
+	depends on OF
+	depends on NVMEM
+	help
+	  Allow block devices (or partitions) to act as NVMEM providers,
+	  typically used with eMMC to store MAC addresses or Wi-Fi
+	  calibration data on embedded devices.
+
 source "block/partitions/Kconfig"
 
 config BLK_PM
diff --git a/block/Makefile b/block/Makefile
index 7dce2e44276c4274c11a0a61121c83d9c43d6e0c..d7ac389e71902bc091a8800ea266190a43b3e63d 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -36,3 +36,4 @@ obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= blk-crypto.o blk-crypto-profile.o \
 					   blk-crypto-sysfs.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
 obj-$(CONFIG_BLOCK_HOLDER_DEPRECATED)	+= holder.o
+obj-$(CONFIG_BLK_NVMEM)                += blk-nvmem.o
diff --git a/block/blk-nvmem.c b/block/blk-nvmem.c
new file mode 100644
index 0000000000000000000000000000000000000000..49e9b5d4410d5e935c4ad9674c6909453fe027ff
--- /dev/null
+++ b/block/blk-nvmem.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * block device NVMEM provider
+ *
+ * Copyright (c) 2024 Daniel Golle <daniel@makrotopia.org>
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ *
+ * Useful on devices using a partition on an eMMC for MAC addresses or
+ * Wi-Fi calibration EEPROM data.
+ */
+
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/file.h>
+#include <linux/nvmem-provider.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/of.h>
+#include <linux/pagemap.h>
+#include <linux/property.h>
+
+#include "blk.h"
+
+static int blk_nvmem_reg_read(void *priv, unsigned int from, void *val, size_t bytes)
+{
+	dev_t devt = (dev_t)(uintptr_t)priv;
+	size_t bytes_left = bytes;
+	loff_t pos = from;
+	int ret = 0;
+
+	struct file *bdev_file __free(fput) =
+		bdev_file_open_by_dev(devt, BLK_OPEN_READ, NULL, NULL);
+	if (IS_ERR(bdev_file))
+		return PTR_ERR(bdev_file);
+
+	while (bytes_left) {
+		pgoff_t f_index = pos >> PAGE_SHIFT;
+		struct folio *folio;
+		size_t folio_off;
+		size_t to_read;
+
+		folio = read_mapping_folio(bdev_file->f_mapping, f_index, NULL);
+		if (IS_ERR(folio)) {
+			ret = PTR_ERR(folio);
+			break;
+		}
+
+		folio_off = offset_in_folio(folio, pos);
+		to_read = min(bytes_left, folio_size(folio) - folio_off);
+		memcpy_from_folio(val, folio, folio_off, to_read);
+		pos += to_read;
+		bytes_left -= to_read;
+		val += to_read;
+		folio_put(folio);
+	}
+
+	return ret;
+}
+
+int blk_nvmem_add(struct block_device *bdev)
+{
+	struct device *dev = &bdev->bd_device;
+	struct nvmem_config config = {};
+
+	/* skip devices which do not have a device tree node */
+	if (!dev_of_node(dev))
+		return 0;
+
+	/* skip devices without an nvmem layout defined */
+	struct device_node *child __free(device_node) =
+		of_get_child_by_name(dev_of_node(dev), "nvmem-layout");
+	if (!child && !of_device_is_compatible(dev_of_node(dev), "fixed-layout"))
+		return 0;
+
+	/*
+	 * skip block device too large to be represented as NVMEM devices,
+	 * nvmem_config.size is a signed int
+	 */
+	if (bdev_nr_bytes(bdev) > INT_MAX) {
+		dev_warn(dev, "block device too large to be an NVMEM provider\n");
+		return 0;
+	}
+
+	config.id = NVMEM_DEVID_NONE;
+	config.dev = dev;
+	config.name = dev_name(dev);
+	config.owner = THIS_MODULE;
+	config.priv = (void *)(uintptr_t)dev->devt;
+	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(dev->fwnode);
+
+	bdev->bd_nvmem = nvmem_register(&config);
+	if (IS_ERR(bdev->bd_nvmem))
+		return dev_err_probe(dev, PTR_ERR(bdev->bd_nvmem),
+				     "Failed to register NVMEM device\n");
+
+	return 0;
+}
+
+void blk_nvmem_del(struct block_device *bdev)
+{
+	nvmem_unregister(bdev->bd_nvmem);
+	bdev->bd_nvmem = NULL;
+}
diff --git a/block/blk.h b/block/blk.h
index ec4674cdf2ead4fd259ff5fc42401f591e684ee9..ed0c10168ba7be10855509637f824a9cea2b9ccb 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -757,4 +757,12 @@ static inline void blk_debugfs_unlock(struct request_queue *q,
 	memalloc_noio_restore(memflags);
 }
 
+#ifdef CONFIG_BLK_NVMEM
+int blk_nvmem_add(struct block_device *bdev);
+void blk_nvmem_del(struct block_device *bdev);
+#else
+static inline int blk_nvmem_add(struct block_device *bdev) { return 0; }
+static inline void blk_nvmem_del(struct block_device *bdev) {}
+#endif
+
 #endif /* BLK_INTERNAL_H */
diff --git a/block/genhd.c b/block/genhd.c
index 7d6854fd28e95ae9134309679a7c6a937f5b7db8..1b2382de6fb30c1e5f60f45c04dc03ed3bf5d5f2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -421,6 +421,8 @@ static void add_disk_final(struct gendisk *disk)
 		 */
 		dev_set_uevent_suppress(ddev, 0);
 		disk_uevent(disk, KOBJ_ADD);
+
+		blk_nvmem_add(disk->part0);
 	}
 
 	blk_apply_bdi_limits(disk->bdi, &disk->queue->limits);
@@ -704,6 +706,8 @@ static void __del_gendisk(struct gendisk *disk)
 
 	disk_del_events(disk);
 
+	blk_nvmem_del(disk->part0);
+
 	/*
 	 * Prevent new openers by unlinked the bdev inode.
 	 */
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 8808ee76e73c09e0ceaac41ba59e86fb0c4efc64..6ed173c649025b95cce9253b27f68f2c7dbab8eb 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -15,6 +15,7 @@
 struct bio_set;
 struct bio;
 struct bio_integrity_payload;
+struct nvmem_device;
 struct page;
 struct io_context;
 struct cgroup_subsys_state;
@@ -73,6 +74,9 @@ struct block_device {
 	int			bd_writers;
 #ifdef CONFIG_SECURITY
 	void			*bd_security;
+#endif
+#ifdef CONFIG_BLK_NVMEM
+	struct nvmem_device	*bd_nvmem;
 #endif
 	/*
 	 * keep this out-of-line as it's both big and not needed in the fast

-- 
2.34.1