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

[Neil Armstrong <narmstrong@baylibre.com>]

On 13/05/2020 12:34, Srinivas Kandagatla wrote:
> 
> 
> 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?

It can be rewritten, and needs the password to read & write.

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

The only way to know it's unlock is reading back the password when unlocked.

> 
>>
>> 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?

Will drop

> 
>> +#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.

Ok

> 
>> +
>> +    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.

Ok

> 
> 
>> +    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!

Ok

> 
>> +    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");
>>

Thanks for the review.

Neil

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