Re: [PATCH v6 3/7] mtd: spi-nor: sfdp: expose the SFDP as a read-only NVMEM device

Hi Michael,

On 7/29/26 13:31, Michael Walle wrote:

On Wed Jul 29, 2026 at 6:30 AM CEST, Manikandan Muralidharan wrote:
..

quoted

+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 (compatible "jedec,sfdp"). This lets
+ * generic (fixed-layout) or vendor (nvmem-layout) cells reference any SFDP
+ * data. The device is only registered when a child node with the "jedec,sfdp"
+ * compatible is described in the device tree.
+ *
+ * Return: 0 on success or if there is nothing to do, -errno otherwise.
+ */
+static 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_compatible_child(dev_of_node(dev), "jedec,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;

Sorry I've missed that in the previous version. I guess we do that
because we hand the device_node to nvmem. But shouldn't it be part
of the NVMEM framework to do a of_node_get()?

Yes, You're right — NVMEM doesn't take its own reference on config.of_node.

quoted

+
+	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_reg_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");
+	}
+

so we can do a of_node_put() here?

I'll follow that in v7 and drop the devm_add_action_or_reset().

-michael

quoted

+	dev_dbg(dev, "exposed %d-byte SFDP as an NVMEM device\n", config.size);
+
+	return 0;
+}
+

-- 
Thanks and Regards,
Manikandan M.