nvmem: Add driver for the eeprom in qnap-mcu controllers

The qnap-mcu also has an eeprom connected to it, that contains some
specific product-information like the mac addresses for the network
interfaces.

Add a nvmem driver for it.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Srinivas Kandagatla <srini@kernel.org>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://patch.msgid.link/20251114110636.143268-4-srini@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/Kconfig

@@ -285,6 +285,15 @@ config NVMEM_QCOM_SEC_QFPROM
           This driver can also be built as a module. If so, the module will be called
           nvmem_sec_qfprom.
 
+config NVMEM_QNAP_MCU_EEPROM
+	tristate "QNAP MCU EEPROM Support"
+	depends on MFD_QNAP_MCU
+	help
+	  Say y here to enable support for accessing the EEPROM attached to
+	  QNAP MCU devices. This EEPROM contains additional runtime device
+	  information, like MAC addresses for ethernet devices that do not
+	  contain their own mac storage.
+
 config NVMEM_RAVE_SP_EEPROM
 	tristate "Rave SP EEPROM Support"
 	depends on RAVE_SP_CORE

drivers/nvmem/Makefile

@@ -56,6 +56,8 @@ obj-$(CONFIG_NVMEM_QCOM_QFPROM)		+= nvmem_qfprom.o
 nvmem_qfprom-y				:= qfprom.o
 obj-$(CONFIG_NVMEM_QCOM_SEC_QFPROM)	+= nvmem_sec_qfprom.o
 nvmem_sec_qfprom-y			:= sec-qfprom.o
+obj-$(CONFIG_NVMEM_QNAP_MCU_EEPROM)	+= nvmem-qnap-mcu-eeprom.o
+nvmem-qnap-mcu-eeprom-y			:= qnap-mcu-eeprom.o
 obj-$(CONFIG_NVMEM_RAVE_SP_EEPROM)	+= nvmem-rave-sp-eeprom.o
 nvmem-rave-sp-eeprom-y			:= rave-sp-eeprom.o
 obj-$(CONFIG_NVMEM_RCAR_EFUSE)		+= nvmem-rcar-efuse.o

drivers/nvmem/qnap-mcu-eeprom.c

@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * ee1004 - driver for DDR4 SPD EEPROMs
+ *
+ * Copyright (C) 2017-2019 Jean Delvare
+ *
+ * Based on the at24 driver:
+ * Copyright (C) 2005-2007 David Brownell
+ * Copyright (C) 2008 Wolfram Sang, Pengutronix
+ */
+
+#include <linux/mfd/qnap-mcu.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+/* Determined by trial and error until read anomalies appeared */
+#define QNAP_MCU_EEPROM_SIZE		256
+#define QNAP_MCU_EEPROM_BLOCK_SIZE	32
+
+static int qnap_mcu_eeprom_read_block(struct qnap_mcu *mcu, unsigned int offset,
+				      void *val, size_t bytes)
+{
+	const u8 cmd[] = { 0xf7, 0xa1, offset, bytes };
+	u8 *reply;
+	int ret = 0;
+
+	reply = kzalloc(bytes + sizeof(cmd), GFP_KERNEL);
+	if (!reply)
+		return -ENOMEM;
+
+	ret = qnap_mcu_exec(mcu, cmd, sizeof(cmd), reply, bytes + sizeof(cmd));
+	if (ret)
+		goto out;
+
+	/* First bytes must mirror the sent command */
+	if (memcmp(cmd, reply, sizeof(cmd))) {
+		ret = -EIO;
+		goto out;
+	}
+
+	memcpy(val, reply + sizeof(cmd), bytes);
+
+out:
+	kfree(reply);
+	return ret;
+}
+
+static int qnap_mcu_eeprom_read(void *priv, unsigned int offset, void *val, size_t bytes)
+{
+	struct qnap_mcu *mcu = priv;
+	int pos = 0, ret;
+	u8 *buf = val;
+
+	if (unlikely(!bytes))
+		return 0;
+
+	while (bytes > 0) {
+		size_t to_read = (bytes > QNAP_MCU_EEPROM_BLOCK_SIZE) ?
+						QNAP_MCU_EEPROM_BLOCK_SIZE : bytes;
+
+		ret = qnap_mcu_eeprom_read_block(mcu, offset + pos, &buf[pos], to_read);
+		if (ret < 0)
+			return ret;
+
+		pos += to_read;
+		bytes -= to_read;
+	}
+
+	return 0;
+}
+
+static int qnap_mcu_eeprom_probe(struct platform_device *pdev)
+{
+	struct qnap_mcu *mcu = dev_get_drvdata(pdev->dev.parent);
+	struct nvmem_config nvcfg = {};
+	struct nvmem_device *ndev;
+
+	nvcfg.dev = &pdev->dev;
+	nvcfg.of_node = pdev->dev.parent->of_node;
+	nvcfg.name = dev_name(&pdev->dev);
+	nvcfg.id = NVMEM_DEVID_NONE;
+	nvcfg.owner = THIS_MODULE;
+	nvcfg.type = NVMEM_TYPE_EEPROM;
+	nvcfg.read_only = true;
+	nvcfg.root_only = false;
+	nvcfg.reg_read = qnap_mcu_eeprom_read;
+	nvcfg.size = QNAP_MCU_EEPROM_SIZE,
+	nvcfg.word_size = 1,
+	nvcfg.stride = 1,
+	nvcfg.priv = mcu,
+
+	ndev = devm_nvmem_register(&pdev->dev, &nvcfg);
+	if (IS_ERR(ndev))
+		return PTR_ERR(ndev);
+
+	return 0;
+}
+
+static struct platform_driver qnap_mcu_eeprom_driver = {
+	.probe = qnap_mcu_eeprom_probe,
+	.driver = {
+		.name = "qnap-mcu-eeprom",
+	},
+};
+module_platform_driver(qnap_mcu_eeprom_driver);
+
+MODULE_AUTHOR("Heiko Stuebner <heiko@sntech.de>");
+MODULE_DESCRIPTION("QNAP MCU EEPROM driver");
+MODULE_LICENSE("GPL");