[RFC PATCH 4/4] mtd: core: add OTP nvmem provider support

[Michael Walle]

Flash OTP regions can already be read via user space. Some boards have
their serial number or MAC addresses stored in the OTP regions. Add
support for them being a (read-only) nvmem provider.

The API to read the OTP data is already in place. It distinguishes
between factory and user OTP, thus there are up to two different
providers.

Signed-off-by: Michael Walle <michael at walle.cc>
---
 drivers/mtd/mtdcore.c   | 149 ++++++++++++++++++++++++++++++++++++++++
 include/linux/mtd/mtd.h |   2 +
 2 files changed, 151 insertions(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 432769caae04..300340973561 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -776,6 +776,147 @@ static void mtd_set_dev_defaults(struct mtd_info *mtd)
 	mutex_init(&mtd->master.chrdev_lock);
 }
 
+static ssize_t mtd_otp_size(struct mtd_info *mtd, bool is_user)
+{
+	struct otp_info *info = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	ssize_t size = 0;
+	unsigned int i;
+	size_t retlen;
+	int ret;
+
+	if (is_user)
+		ret = mtd_get_user_prot_info(mtd, PAGE_SIZE, &retlen, info);
+	else
+		ret = mtd_get_fact_prot_info(mtd, PAGE_SIZE, &retlen, info);
+	if (ret)
+		goto err;
+
+	for (i = 0; i < retlen / sizeof(*info); i++) {
+		size += info->length;
+		info++;
+	}
+
+	kfree(info);
+	return size;
+
+err:
+	kfree(info);
+	return ret;
+}
+
+static struct nvmem_device *mtd_otp_nvmem_register(struct mtd_info *mtd,
+						   const char *name, int size,
+						   nvmem_reg_read_t reg_read,
+						   const char *compatible)
+{
+	struct nvmem_device *nvmem = NULL;
+	struct nvmem_config config = {};
+	struct device_node *np;
+
+	/* DT binding is optional */
+	np = of_get_compatible_child(mtd->dev.of_node, compatible);
+
+	/* OTP nvmem will be registered on the physical device */
+	config.dev = mtd->dev.parent;
+	config.name = name;
+	config.id = NVMEM_DEVID_NONE;
+	config.owner = THIS_MODULE;
+	config.type = NVMEM_TYPE_OTP;
+	config.root_only = true;
+	config.reg_read = reg_read;
+	config.size = size;
+	config.of_node = np;
+	config.priv = mtd;
+
+	nvmem = nvmem_register(&config);
+	/* Just ignore if there is no NVMEM support in the kernel */
+	if (IS_ERR(nvmem) && PTR_ERR(nvmem) == -EOPNOTSUPP)
+		nvmem = NULL;
+
+	of_node_put(np);
+
+	return nvmem;
+}
+
+static int mtd_nvmem_user_otp_reg_read(void *priv, unsigned int offset,
+				       void *val, size_t bytes)
+{
+	struct mtd_info *mtd = priv;
+	size_t retlen;
+	int ret;
+
+	ret = mtd_read_user_prot_reg(mtd, offset, bytes, &retlen, val);
+	if (ret)
+		return ret;
+
+	return retlen == bytes ? 0 : -EIO;
+}
+
+static int mtd_nvmem_fact_otp_reg_read(void *priv, unsigned int offset,
+				       void *val, size_t bytes)
+{
+	struct mtd_info *mtd = priv;
+	size_t retlen;
+	int ret;
+
+	ret = mtd_read_fact_prot_reg(mtd, offset, bytes, &retlen, val);
+	if (ret)
+		return ret;
+
+	return retlen == bytes ? 0 : -EIO;
+}
+
+static int mtd_otp_nvmem_add(struct mtd_info *mtd)
+{
+	struct nvmem_device *nvmem;
+	ssize_t size;
+	int err;
+
+	if (mtd->_get_user_prot_info && mtd->_read_user_prot_reg) {
+		size = mtd_otp_size(mtd, true);
+		if (size < 0)
+			return size;
+
+		if (size > 0) {
+			nvmem = mtd_otp_nvmem_register(mtd, "user-otp", size,
+						       mtd_nvmem_user_otp_reg_read,
+						       "mtd-user-otp");
+			if (IS_ERR(nvmem)) {
+				dev_err(&mtd->dev, "Failed to register OTP NVMEM device\n");
+				return PTR_ERR(nvmem);
+			}
+			mtd->otp_user_nvmem = nvmem;
+		}
+	}
+
+	if (mtd->_get_fact_prot_info && mtd->_read_fact_prot_reg) {
+		size = mtd_otp_size(mtd, false);
+		if (size < 0) {
+			err = size;
+			goto err;
+		}
+
+		if (size > 0) {
+			nvmem = mtd_otp_nvmem_register(mtd, "factory-otp", size,
+						       mtd_nvmem_fact_otp_reg_read,
+						       "mtd-factory-otp");
+			if (IS_ERR(nvmem)) {
+				dev_err(&mtd->dev, "Failed to register OTP NVMEM device\n");
+				err = PTR_ERR(nvmem);
+				goto err;
+			}
+			mtd->otp_factory_nvmem = nvmem;
+		}
+	}
+
+	return 0;
+
+err:
+	if (mtd->otp_user_nvmem)
+		nvmem_unregister(mtd->otp_user_nvmem);
+	return err;
+}
+
 /**
  * mtd_device_parse_register - parse partitions and register an MTD device.
  *
@@ -851,6 +992,8 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
 		register_reboot_notifier(&mtd->reboot_notifier);
 	}
 
+	ret = mtd_otp_nvmem_add(mtd);
+
 out:
 	if (ret && device_is_registered(&mtd->dev))
 		del_mtd_device(mtd);
@@ -872,6 +1015,12 @@ int mtd_device_unregister(struct mtd_info *master)
 	if (master->_reboot)
 		unregister_reboot_notifier(&master->reboot_notifier);
 
+	if (master->otp_user_nvmem)
+		nvmem_unregister(master->otp_user_nvmem);
+
+	if (master->otp_factory_nvmem)
+		nvmem_unregister(master->otp_factory_nvmem);
+
 	err = del_mtd_partitions(master);
 	if (err)
 		return err;
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 4aac200ca8b5..71e751d18c22 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -379,6 +379,8 @@ struct mtd_info {
 	int usecount;
 	struct mtd_debug_info dbg;
 	struct nvmem_device *nvmem;
+	struct nvmem_device *otp_user_nvmem;
+	struct nvmem_device *otp_factory_nvmem;
 
 	/*
 	 * Parent device from the MTD partition point of view.
-- 
2.20.1