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

[Manikandan.M at microchip.com]

Hi Michael,

On 7/29/26 13:31, Michael Walle wrote:
> On Wed Jul 29, 2026 at 6:30 AM CEST, Manikandan Muralidharan wrote:
> ..
> 
>> +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.
>> +
>> +	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
> 
>> +	dev_dbg(dev, "exposed %d-byte SFDP as an NVMEM device\n", config.size);
>> +
>> +	return 0;
>> +}
>> +


-- 
Thanks and Regards,
Manikandan M.