[PATCH v4 3/7] mtd: spi-nor: sfdp: expose the SFDP as a read-only NVMEM device

[Manikandan Muralidharan <manikandan.m@microchip.com>]

Register the cached SFDP as a read-only NVMEM device rooted at the
flash's "sfdp" child node, exposing it in on-flash byte order. This lets
NVMEM cells reference any SFDP data: a fixed-layout for parameters at a
known offset, or an nvmem-layout parser for vendor data whose location
must be discovered at runtime. The device is only registered when an
"sfdp" node is present in the device tree.

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
---
 drivers/mtd/spi-nor/core.c |  5 +++
 drivers/mtd/spi-nor/core.h |  1 +
 drivers/mtd/spi-nor/sfdp.c | 83 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 89 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ccf4396cdcd0..e04ba3e3dee9 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3204,6 +3204,11 @@ static int spi_nor_init_params(struct spi_nor *nor)
 		spi_nor_init_params_deprecated(nor);
 	}
 
+	/* Expose the SFDP as an NVMEM device. */
+	ret = spi_nor_register_sfdp_nvmem(nor);
+	if (ret)
+		return ret;
+
 	ret = spi_nor_late_init_params(nor);
 	if (ret)
 		return ret;
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index ba2d1a862c9d..0a6484298c5c 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -698,6 +698,7 @@ int spi_nor_controller_ops_write_reg(struct spi_nor *nor, u8 opcode,
 
 int spi_nor_check_sfdp_signature(struct spi_nor *nor);
 int spi_nor_parse_sfdp(struct spi_nor *nor);
+int spi_nor_register_sfdp_nvmem(struct spi_nor *nor);
 
 static inline struct spi_nor *mtd_to_spi_nor(struct mtd_info *mtd)
 {
diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
index 4600983cb579..2df818bca6b5 100644
--- a/drivers/mtd/spi-nor/sfdp.c
+++ b/drivers/mtd/spi-nor/sfdp.c
@@ -6,6 +6,8 @@
 
 #include <linux/bitfield.h>
 #include <linux/mtd/spi-nor.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
 #include <linux/slab.h>
 #include <linux/sort.h>
 
@@ -1612,3 +1614,84 @@ int spi_nor_parse_sfdp(struct spi_nor *nor)
 	kfree(param_headers);
 	return err;
 }
+
+static int spi_nor_sfdp_nvmem_read(void *priv, unsigned int offset,
+				   void *val, size_t bytes)
+{
+	struct spi_nor *nor = priv;
+	struct sfdp *sfdp = nor->sfdp;
+	size_t sfdp_size = sfdp->num_dwords * sizeof(*sfdp->dwords);
+
+	if (offset >= sfdp_size || bytes > sfdp_size - offset)
+		return -EINVAL;
+
+	/* The cached SFDP is kept in on-flash (little-endian) byte order. */
+	memcpy(val, (u8 *)sfdp->dwords + offset, bytes);
+
+	return 0;
+}
+
+static void spi_nor_sfdp_nvmem_put_np(void *data)
+{
+	of_node_put(data);
+}
+
+/**
+ * spi_nor_register_sfdp_nvmem() - expose the SFDP as a read-only NVMEM device
+ * @nor:	pointer to a 'struct spi_nor'
+ *
+ * Expose the whole SFDP, in on-flash byte order, as a read-only NVMEM device
+ * rooted at the flash's "sfdp" child node. This lets generic (fixed-layout) or
+ * vendor (nvmem-layout) cells reference any SFDP data. The device is only
+ * registered when an "sfdp" node is described in the device tree.
+ *
+ * Return: 0 on success or if there is nothing to do, -errno otherwise.
+ */
+int spi_nor_register_sfdp_nvmem(struct spi_nor *nor)
+{
+	struct device *dev = nor->dev;
+	struct nvmem_config config = { };
+	struct nvmem_device *nvmem;
+	struct device_node *np;
+	int ret;
+
+	if (!nor->sfdp)
+		return 0;
+
+	np = of_get_child_by_name(dev_of_node(dev), "sfdp");
+	if (!np)
+		return 0;
+
+	/*
+	 * Register the put before devm_nvmem_register() so it runs last on
+	 * detach, after the NVMEM device that uses the node is gone.
+	 */
+	ret = devm_add_action_or_reset(dev, spi_nor_sfdp_nvmem_put_np, np);
+	if (ret)
+		return ret;
+
+	config.dev = dev;
+	config.of_node = np;
+	config.name = "sfdp";
+	config.id = NVMEM_DEVID_AUTO;
+	config.owner = THIS_MODULE;
+	config.read_only = true;
+	config.word_size = 1;
+	config.stride = 1;
+	config.size = (int)(nor->sfdp->num_dwords * sizeof(*nor->sfdp->dwords));
+	config.reg_read = spi_nor_sfdp_nvmem_read;
+	config.priv = nor;
+
+	nvmem = devm_nvmem_register(dev, &config);
+	if (IS_ERR(nvmem)) {
+		/* NVMEM support is optional. */
+		if (PTR_ERR(nvmem) == -EOPNOTSUPP)
+			return 0;
+		return dev_err_probe(dev, PTR_ERR(nvmem),
+				     "failed to register SFDP NVMEM device\n");
+	}
+
+	dev_dbg(dev, "exposed %d-byte SFDP as an NVMEM device\n", config.size);
+
+	return 0;
+}
-- 
2.43.0