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

From: Srinivas Kandagatla
Date: Fri May 15 2020 - 06:55:17 EST



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@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
ÂÂÂÂÂÂÂ To compile this driver as a module, choose M here: the module
ÂÂÂÂÂÂÂ will be called nvmem_jz4780_efuse.
 +config NVMEM_KHADAS_MCU_USER_MEM
+ÂÂÂ tristate "Khadas MCU User programmable memory support"
+ÂÂÂ depends on MFD_KHADAS_MCU
+ÂÂÂ depends on REGMAP
+ÂÂÂ help
+ÂÂÂÂÂ This is a driver for the MCU User programmable memory
+ÂÂÂÂÂ available on the Khadas VIM and Edge boards.
+
 config NVMEM_LPC18XX_EEPROM
ÂÂÂÂÂ tristate "NXP LPC18XX EEPROM Memory Support"
ÂÂÂÂÂ 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-$(CONFIG_NVMEM_IMX_OCOTP_SCU)ÂÂÂ += nvmem-imx-ocotp-scu.o
 nvmem-imx-ocotp-scu-y := imx-ocotp-scu.o
 obj-$(CONFIG_JZ4780_EFUSE) += nvmem_jz4780_efuse.o
 nvmem_jz4780_efuse-y := jz4780-efuse.o
+obj-$(CONFIG_NVMEM_KHADAS_MCU_USER_MEM)ÂÂÂ += nvmem-khadas-mcu-user-mem.o
+nvmem-khadas-mcu-user-mem-yÂÂÂ := khadas-mcu-user-mem.o
 obj-$(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>

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,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ void *val, size_t bytes)
+{
+ÂÂÂ struct khadas_mcu *khadas_mcu = context;
+
+ÂÂÂ return regmap_bulk_read(khadas_mcu->map,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ KHADAS_MCU_USER_DATA_0_REG + offset,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ val, bytes);
+}
+
+static int khadas_mcu_user_mem_write(void *context, unsigned int offset,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ void *val, size_t bytes)
+{
+ÂÂÂ struct khadas_mcu *khadas_mcu = context;
+
+ÂÂÂ return regmap_bulk_write(khadas_mcu->map,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ KHADAS_MCU_USER_DATA_0_REG + offset,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ val, bytes);
+}
+
+static ssize_t password_store(struct device *dev, struct device_attribute *attr,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ const char *buf, size_t count)
+{
+ÂÂÂ struct khadas_mcu *khadas_mcu = dev_get_drvdata(dev);
+ÂÂÂ int i, ret;
+
+ÂÂÂ if (count < 6)
+ÂÂÂÂÂÂÂ return -EINVAL;

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

Ok


+
+ÂÂÂ ret = regmap_write(khadas_mcu->map, KHADAS_MCU_PASSWD_START_REG, 1);
+ÂÂÂ if (ret)
+ÂÂÂÂÂÂÂ return ret;
+
+ÂÂÂ for (i = 0 ; i < 6 ; ++i) {
+ÂÂÂÂÂÂÂ ret = regmap_write(khadas_mcu->map,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ KHADAS_MCU_CHECK_USER_PASSWD_REG,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ buf[i]);
+ÂÂÂÂÂÂÂ if (ret)
+ÂÂÂÂÂÂÂÂÂÂÂ goto out;
+ÂÂÂ }
+
+ÂÂÂ ret = regmap_write(khadas_mcu->map, KHADAS_MCU_PASSWD_START_REG, 0);
+ÂÂÂ if (ret)
+ÂÂÂÂÂÂÂ return ret;
+
+ÂÂÂ return count;
+out:
+ÂÂÂ regmap_write(khadas_mcu->map, KHADAS_MCU_PASSWD_START_REG, 0);
+
+ÂÂÂ return ret;
+}
+
+static DEVICE_ATTR_WO(password);
+
+static struct attribute *khadas_mcu_user_mem_sysfs_attributes[] = {
+ÂÂÂ &dev_attr_password.attr,
+ÂÂÂ NULL,
+};
+
+static const struct attribute_group khadas_mcu_user_mem_sysfs_attr_group = {
+ÂÂÂ .attrs = khadas_mcu_user_mem_sysfs_attributes,
+};
+
+static int khadas_mcu_user_mem_probe(struct platform_device *pdev)
+{
+ÂÂÂ 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



+ÂÂÂ struct device *dev = &pdev->dev;
+ÂÂÂ struct nvmem_device *nvmem;
+ÂÂÂ struct nvmem_config *econfig;
+
+ÂÂÂ econfig = devm_kzalloc(dev, sizeof(*econfig), GFP_KERNEL);
+ÂÂÂ if (!econfig)
+ÂÂÂÂÂÂÂ return -ENOMEM;
+
+ÂÂÂ econfig->dev = pdev->dev.parent;
+ÂÂÂ econfig->name = dev_name(pdev->dev.parent);
+ÂÂÂ econfig->stride = 1;
+ÂÂÂ econfig->word_size = 1;
+ÂÂÂ econfig->reg_read = khadas_mcu_user_mem_read;
+ÂÂÂ econfig->reg_write = khadas_mcu_user_mem_write;
+ÂÂÂ econfig->size = 56;
define 56 to make it more readable!

Ok


+ÂÂÂ econfig->priv = khadas_mcu;
+
+ÂÂÂ platform_set_drvdata(pdev, khadas_mcu);
+
+ÂÂÂ nvmem = devm_nvmem_register(&pdev->dev, econfig);
+ÂÂÂ if (IS_ERR(nvmem))
+ÂÂÂÂÂÂÂ return PTR_ERR(nvmem);
+
+ÂÂÂ return sysfs_create_group(&pdev->dev.kobj,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ &khadas_mcu_user_mem_sysfs_attr_group);
+}
+
+static const struct platform_device_id khadas_mcu_user_mem_id_table[] = {
+ÂÂÂ { .name = "khadas-mcu-user-mem", },
+ÂÂÂ {},
+};
+MODULE_DEVICE_TABLE(platform, khadas_mcu_user_mem_id_table);
+
+static struct platform_driver khadas_mcu_user_mem_driver = {
+ÂÂÂ .probe = khadas_mcu_user_mem_probe,
+ÂÂÂ .driver = {
+ÂÂÂÂÂÂÂ .name = "khadas-mcu-user-mem",
+ÂÂÂ },
+ÂÂÂ .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");


Thanks for the review.

Neil