mtd: add support for reading MTD devices via the nvmem API

Allow drivers that use the nvmem API to read data stored on MTD devices.
For this the mtd devices are registered as read-only NVMEM providers.

We don't support device tree systems for now.

Signed-off-by: Alban Bedel <albeu@free.fr>
[Bartosz:
  - include linux/nvmem-provider.h
  - set the name of the nvmem provider
  - set no_of_node to true in nvmem_config
  - don't check the return value of nvmem_unregister() - it cannot fail
  - tweaked the commit message]
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 57 insertions, 0 deletions

diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
index c77f537323ec..efbe7a6f1d8f 100644
--- a/drivers/mtd/Kconfig
+++ b/drivers/mtd/Kconfig
@@ -1,5 +1,6 @@
 menuconfig MTD
 	tristate "Memory Technology Device (MTD) support"
+	imply NVMEM
 	help
 	  Memory Technology Devices are flash, RAM and similar chips, often
 	  used for solid state file systems on embedded devices. This option
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 97ac219c082e..5f1053d995b0 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -41,6 +41,7 @@
 #include <linux/reboot.h>
 #include <linux/leds.h>
 #include <linux/debugfs.h>
+#include <linux/nvmem-provider.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
@@ -488,6 +489,50 @@ int mtd_pairing_groups(struct mtd_info *mtd)
 }
 EXPORT_SYMBOL_GPL(mtd_pairing_groups);
 
+static int mtd_nvmem_reg_read(void *priv, unsigned int offset,
+			      void *val, size_t bytes)
+{
+	struct mtd_info *mtd = priv;
+	size_t retlen;
+	int err;
+
+	err = mtd_read(mtd, offset, bytes, &retlen, val);
+	if (err && err != -EUCLEAN)
+		return err;
+
+	return retlen == bytes ? 0 : -EIO;
+}
+
+static int mtd_nvmem_add(struct mtd_info *mtd)
+{
+	struct nvmem_config config = {};
+
+	config.dev = &mtd->dev;
+	config.name = mtd->name;
+	config.owner = THIS_MODULE;
+	config.reg_read = mtd_nvmem_reg_read;
+	config.size = mtd->size;
+	config.word_size = 1;
+	config.stride = 1;
+	config.read_only = true;
+	config.root_only = true;
+	config.no_of_node = true;
+	config.priv = mtd;
+
+	mtd->nvmem = nvmem_register(&config);
+	if (IS_ERR(mtd->nvmem)) {
+		/* Just ignore if there is no NVMEM support in the kernel */
+		if (PTR_ERR(mtd->nvmem) == -ENOSYS) {
+			mtd->nvmem = NULL;
+		} else {
+			dev_err(&mtd->dev, "Failed to register NVMEM device\n");
+			return PTR_ERR(mtd->nvmem);
+		}
+	}
+
+	return 0;
+}
+
 static struct dentry *dfs_dir_mtd;
 
 /**
@@ -570,6 +615,11 @@ int add_mtd_device(struct mtd_info *mtd)
 	if (error)
 		goto fail_added;
 
+	/* Add the nvmem provider */
+	error = mtd_nvmem_add(mtd);
+	if (error)
+		goto fail_nvmem_add;
+
 	if (!IS_ERR_OR_NULL(dfs_dir_mtd)) {
 		mtd->dbg.dfs_dir = debugfs_create_dir(dev_name(&mtd->dev), dfs_dir_mtd);
 		if (IS_ERR_OR_NULL(mtd->dbg.dfs_dir)) {
@@ -595,6 +645,8 @@ int add_mtd_device(struct mtd_info *mtd)
 	__module_get(THIS_MODULE);
 	return 0;
 
+fail_nvmem_add:
+	device_unregister(&mtd->dev);
 fail_added:
 	of_node_put(mtd_get_of_node(mtd));
 	idr_remove(&mtd_idr, i);
@@ -637,6 +689,10 @@ int del_mtd_device(struct mtd_info *mtd)
 		       mtd->index, mtd->name, mtd->usecount);
 		ret = -EBUSY;
 	} else {
+		/* Try to remove the NVMEM provider */
+		if (mtd->nvmem)
+			nvmem_unregister(mtd->nvmem);
+
 		device_unregister(&mtd->dev);
 
 		idr_remove(&mtd_idr, mtd->index);