[RFC 4/8] nvmem: add support for the Khadas MCU Programmable User Memory

[Neil Armstrong]

The new Khadas VIM2, VIM3 and Edge boards embeds an on-board microcontroller
offering a 56bytes User Programmable NVMEM array.

This array needs a password to be writable, thus a password sysfs file
has been added on the device node to unlock the NVMEM.

The default 6bytes password id: "Khadas"

This implements the user NVMEM devices as cell of the Khadas MCU MFD driver.

Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
---
 drivers/nvmem/Kconfig               |   8 ++
 drivers/nvmem/Makefile              |   2 +
 drivers/nvmem/khadas-mcu-user-mem.c | 128 ++++++++++++++++++++++++++++
 3 files changed, 138 insertions(+)
 create mode 100644 drivers/nvmem/khadas-mcu-user-mem.c

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index d7b7f6d688e7..92cd4f6aa931 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -67,6 +67,14 @@ config JZ4780_EFUSE
 	  To compile this driver as a module, choose M here: the module
 	  will be called nvmem_jz4780_efuse.
 
+config NVMEM_KHADAS_MCU_USER_MEM
+	tristate "Khadas MCU User programmable memory support"
+	depends on MFD_KHADAS_MCU
+	depends on REGMAP
+	help
+	  This is a driver for the MCU User programmable memory
+	  available on the Khadas VIM and Edge boards.
+
 config NVMEM_LPC18XX_EEPROM
 	tristate "NXP LPC18XX EEPROM Memory Support"
 	depends on ARCH_LPC18XX || COMPILE_TEST
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index a7c377218341..0516a309542d 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -17,6 +17,8 @@ obj-$(CONFIG_NVMEM_IMX_OCOTP_SCU)	+= nvmem-imx-ocotp-scu.o
 nvmem-imx-ocotp-scu-y		:= imx-ocotp-scu.o
 obj-$(CONFIG_JZ4780_EFUSE)		+= nvmem_jz4780_efuse.o
 nvmem_jz4780_efuse-y		:= jz4780-efuse.o
+obj-$(CONFIG_NVMEM_KHADAS_MCU_USER_MEM)	+= nvmem-khadas-mcu-user-mem.o
+nvmem-khadas-mcu-user-mem-y	:= khadas-mcu-user-mem.o
 obj-$(CONFIG_NVMEM_LPC18XX_EEPROM)	+= nvmem_lpc18xx_eeprom.o
 nvmem_lpc18xx_eeprom-y	:= lpc18xx_eeprom.o
 obj-$(CONFIG_NVMEM_LPC18XX_OTP)	+= nvmem_lpc18xx_otp.o
diff --git a/drivers/nvmem/khadas-mcu-user-mem.c b/drivers/nvmem/khadas-mcu-user-mem.c
new file mode 100644
index 000000000000..a1d5ae9a030c
--- /dev/null
+++ b/drivers/nvmem/khadas-mcu-user-mem.c
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for Khadas MCU User programmable Memory
+ *
+ * Copyright (C) 2020 BayLibre SAS
+ * Author(s): Neil Armstrong <narmstrong@xxxxxxxxxxxx>
+ */
+
+#include <linux/clk.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/mfd/khadas-mcu.h>
+#include <linux/regmap.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+static int khadas_mcu_user_mem_read(void *context, unsigned int offset,
+			    void *val, size_t bytes)
+{
+	struct khadas_mcu *khadas_mcu = context;
+
+	return regmap_bulk_read(khadas_mcu->map,
+				KHADAS_MCU_USER_DATA_0_REG + offset,
+				val, bytes);
+}
+
+static int khadas_mcu_user_mem_write(void *context, unsigned int offset,
+			     void *val, size_t bytes)
+{
+	struct khadas_mcu *khadas_mcu = context;
+
+	return regmap_bulk_write(khadas_mcu->map,
+				KHADAS_MCU_USER_DATA_0_REG + offset,
+				val, bytes);
+}
+
+static ssize_t password_store(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t count)
+{
+	struct khadas_mcu *khadas_mcu = dev_get_drvdata(dev);
+	int i, ret;
+
+	if (count < 6)
+		return -EINVAL;
+
+	ret = regmap_write(khadas_mcu->map, KHADAS_MCU_PASSWD_START_REG, 1);
+	if (ret)
+		return ret;
+
+	for (i = 0 ; i < 6 ; ++i) {
+		ret = regmap_write(khadas_mcu->map,
+				   KHADAS_MCU_CHECK_USER_PASSWD_REG,
+				   buf[i]);
+		if (ret)
+			goto out;
+	}
+
+	ret = regmap_write(khadas_mcu->map, KHADAS_MCU_PASSWD_START_REG, 0);
+	if (ret)
+		return ret;
+
+	return count;
+out:
+	regmap_write(khadas_mcu->map, KHADAS_MCU_PASSWD_START_REG, 0);
+
+	return ret;
+}
+
+static DEVICE_ATTR_WO(password);
+
+static struct attribute *khadas_mcu_user_mem_sysfs_attributes[] = {
+	&dev_attr_password.attr,
+	NULL,
+};
+
+static const struct attribute_group khadas_mcu_user_mem_sysfs_attr_group = {
+	.attrs = khadas_mcu_user_mem_sysfs_attributes,
+};
+
+static int khadas_mcu_user_mem_probe(struct platform_device *pdev)
+{
+	struct khadas_mcu *khadas_mcu = dev_get_drvdata(pdev->dev.parent);
+	struct device *dev = &pdev->dev;
+	struct nvmem_device *nvmem;
+	struct nvmem_config *econfig;
+
+	econfig = devm_kzalloc(dev, sizeof(*econfig), GFP_KERNEL);
+	if (!econfig)
+		return -ENOMEM;
+
+	econfig->dev = pdev->dev.parent;
+	econfig->name = dev_name(pdev->dev.parent);
+	econfig->stride = 1;
+	econfig->word_size = 1;
+	econfig->reg_read = khadas_mcu_user_mem_read;
+	econfig->reg_write = khadas_mcu_user_mem_write;
+	econfig->size = 56;
+	econfig->priv = khadas_mcu;
+
+	platform_set_drvdata(pdev, khadas_mcu);
+
+	nvmem = devm_nvmem_register(&pdev->dev, econfig);
+	if (IS_ERR(nvmem))
+		return PTR_ERR(nvmem);
+
+	return sysfs_create_group(&pdev->dev.kobj,
+				  &khadas_mcu_user_mem_sysfs_attr_group);
+}
+
+static const struct platform_device_id khadas_mcu_user_mem_id_table[] = {
+	{ .name = "khadas-mcu-user-mem", },
+	{},
+};
+MODULE_DEVICE_TABLE(platform, khadas_mcu_user_mem_id_table);
+
+static struct platform_driver khadas_mcu_user_mem_driver = {
+	.probe = khadas_mcu_user_mem_probe,
+	.driver = {
+		.name = "khadas-mcu-user-mem",
+	},
+	.id_table = khadas_mcu_user_mem_id_table,
+};
+
+module_platform_driver(khadas_mcu_user_mem_driver);
+
+MODULE_AUTHOR("Neil Armstrong <narmstrong@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Khadas MCU User MEM driver");
+MODULE_LICENSE("GPL v2");
-- 
2.22.0