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

From: "Michael Walle" <mwalle@kernel.org>
To: "Manikandan Muralidharan" <manikandan.m@microchip.com>,
	<pratyush@kernel.org>, <mwalle@kernel.org>,
	<takahiro.kuwano@infineon.com>, <miquel.raynal@bootlin.com>,
	<richard@nod.at>, <vigneshr@ti.com>, <robh@kernel.org>,
	<krzk+dt@kernel.org>, <conor+dt@kernel.org>, <srini@kernel.org>,
	<nicolas.ferre@microchip.com>, <alexandre.belloni@bootlin.com>,
	<claudiu.beznea@tuxon.dev>, <linux@armlinux.org.uk>,
	<richardcochran@gmail.com>, <arnd@arndb.de>, <linusw@kernel.org>,
	<linux-mtd@lists.infradead.org>, <devicetree@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <netdev@vger.kernel.org>
Subject: Re: [PATCH v6 3/7] mtd: spi-nor: sfdp: expose the SFDP as a read-only NVMEM device
Date: Wed, 29 Jul 2026 10:01:59 +0200	[thread overview]
Message-ID: <DKAWBT1F1VM2.1LA8AKQ6B17AE@kernel.org> (raw)
In-Reply-To: <20260729043026.1811147-4-manikandan.m@microchip.com>

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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()?

> +
> +	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?

-michael

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

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