Re: [PATCH v6 5/9] block: implement NVMEM provider
From: Bartosz Golaszewski <brgl@kernel.org>
Date: 2026-06-30 07:59:11
Also in:
linux-arm-msm, linux-block, linux-bluetooth, linux-devicetree, linux-mmc, linux-wireless, lkml
On Mon, 29 Jun 2026 10:55:24 +0200, Loic Poulain [off-list ref] said:
quoted hunk ↗ jump to hunk
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. For now, NVMEM is only registered for the whole disk block device, as the OF node is currently only associated to it. 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> --- block/Kconfig | 9 ++++ block/Makefile | 1 + block/blk-nvmem.c | 111 ++++++++++++++++++++++++++++++++++++++++++++++ block/blk.h | 8 ++++ block/genhd.c | 4 ++ include/linux/blk_types.h | 3 ++ include/linux/blkdev.h | 1 + 7 files changed, 137 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_PMdiff --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.odiff --git a/block/blk-nvmem.c b/block/blk-nvmem.c new file mode 100644 index 0000000000000000000000000000000000000000..4b35a74255059320ef0cbd3c0003f1510bae5733 --- /dev/null +++ b/block/blk-nvmem.c@@ -0,0 +1,111 @@ +// 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. + */ +
Add linux/cleanup.h for __free() and linux/device.h for dev_err_probe().
+#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)
+ 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)) {
+ int ret = PTR_ERR(bdev->bd_nvmem);
+
+ bdev->bd_nvmem = NULL;
+ dev_err_probe(dev, ret, "Failed to register NVMEM device\n");
+ return ret;Just do return dev_err_probe().
quoted hunk ↗ jump to hunk
+ } + + 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..ace6f59b860d0813665b2f62a1c03a1f4be94059 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h@@ -73,6 +73,9 @@ 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 fastdiff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 890128cdea1ce66863c5baa36f3b336ec4550807..f15d2b5bf9e4fd2368b8a70416a978e22c0d4333 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h@@ -30,6 +30,7 @@ struct module; struct request_queue; +struct nvmem_device;
Why is the forward declaration here and not in blk_types.h where it's needed?
struct elevator_queue; struct blk_trace; struct request; -- 2.34.1
With the above nits addressed, LGTM: Reviewed-by: Bartosz Golaszewski <redacted> Bart