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Date: Fri, 15 May 2020 11:55:10 +0100
From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To: Neil Armstrong <narmstrong@...libre.com>
Cc: linux-amlogic@...ts.infradead.org, linux-pm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] nvmem: add support for the Khadas MCU Programmable
User Memory
On 13/05/2020 13:33, Neil Armstrong wrote:
> 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.
Current code has no such checks for every read/write?
and looks very disconnected w.r.t to password and read/writes.
If user attempts to read/write he will not be aware that he should
program the password first!
Also if the password is static or un-changed then why not just
statically program this from the driver rather than providing sysfs file?
I dont see how kernel nvmem read/write interface can make sure that
memory is unlocked?
Who is the real consumer for this provider?
--srini
>
>>
>>>
>>> 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@...libre.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@...libre.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@...libre.com>");
>>> +MODULE_DESCRIPTION("Khadas MCU User MEM driver");
>>> +MODULE_LICENSE("GPL v2");
>>>
>
> Thanks for the review.
>
> Neil
>
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