Re: [PATCH v2 4/6] nvmem: add support for the Khadas MCU Programmable User Memory

From: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
To: Neil Armstrong <narmstrong@baylibre.com>
Cc: linux-amlogic@lists.infradead.org, linux-pm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/6] nvmem: add support for the Khadas MCU Programmable User Memory
Date: Wed, 13 May 2020 11:34:13 +0100	[thread overview]
Message-ID: <09026bde-0ae7-b1a4-835f-bf2481199398@linaro.org> (raw)
In-Reply-To: <20200512132613.31507-5-narmstrong@baylibre.com>

On 12/05/2020 14:26, Neil Armstrong wrote:
> 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.

Is this one time programmable? Or does it need to be unlocked for every 
read/write?

How can you make sure that the memory is unlocked before making attempt 
to read/write?

> 
> 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@baylibre.com>
> ---
>   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@baylibre.com>
> + */
> +
> +#include <linux/clk.h>

Why do we need this header?

> +#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;

Possibly this magic 6 value needs proper define. An additional check 
here for > 6 would be better as well.

> +
> +	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);

You could probably get away with dependency of this structure and the 
header itself by directly getting hold of regmap from parent device.

> +	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;
define 56 to make it more readable!

> +	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@baylibre.com>");
> +MODULE_DESCRIPTION("Khadas MCU User MEM driver");
> +MODULE_LICENSE("GPL v2");
> 