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

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

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

quoted

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.

quoted

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 <redacted>
---
  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

quoted

+#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

quoted

+
+    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

quoted

+    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

quoted

+    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 [off-list ref]");
+MODULE_DESCRIPTION("Khadas MCU User MEM driver");
+MODULE_LICENSE("GPL v2");

Thanks for the review.

Neil