git.openwrt.org Git - openwrt/staging/xback.git/blob

   1 From 9d7eb234ac7a56b88aea8a52ed81553a730fe25c Mon Sep 17 00:00:00 2001
   2 From: Marek Vasut <marex@denx.de>
   3 Date: Fri, 5 Jul 2024 08:48:52 +0100
   4 Subject: [PATCH] nvmem: core: Implement force_ro sysfs attribute
   5
   6 Implement "force_ro" sysfs attribute to allow users to set read-write
   7 devices as read-only and back to read-write from userspace. The choice
   8 of the name is based on MMC core 'force_ro' attribute.
   9
  10 This solves a situation where an AT24 I2C EEPROM with GPIO based nWP
  11 signal may have to be occasionally updated. Such I2C EEPROM device is
  12 usually set as read-only during most of the regular system operation,
  13 but in case it has to be updated in a controlled manner, it could be
  14 unlocked using this new "force_ro" sysfs attribute and then re-locked
  15 again.
  16
  17 The "read-only" DT property and config->read_only configuration is
  18 respected and is used to set default state of the device, read-only
  19 or read-write, for devices which do implement .reg_write function.
  20 For devices which do not implement .reg_write function, the device
  21 is unconditionally read-only and the "force_ro" attribute is not
  22 visible.
  23
  24 Signed-off-by: Marek Vasut <marex@denx.de>
  25 Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
  26 Link: https://lore.kernel.org/r/20240705074852.423202-16-srinivas.kandagatla@linaro.org
  27 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  28 ---
  29  Documentation/ABI/stable/sysfs-bus-nvmem | 17 ++++++++++
  30  drivers/nvmem/core.c                     | 43 ++++++++++++++++++++++++
  31  2 files changed, 60 insertions(+)
  32
  33 --- a/Documentation/ABI/stable/sysfs-bus-nvmem
  34 +++ b/Documentation/ABI/stable/sysfs-bus-nvmem
  35 @@ -1,3 +1,20 @@
  36 +What:          /sys/bus/nvmem/devices/.../force_ro
  37 +Date:          June 2024
  38 +KernelVersion: 6.11
  39 +Contact:       Marek Vasut <marex@denx.de>
  40 +Description:
  41 +               This read/write attribute allows users to set read-write
  42 +               devices as read-only and back to read-write from userspace.
  43 +               This can be used to unlock and relock write-protection of
  44 +               devices which are generally locked, except during sporadic
  45 +               programming operation.
  46 +               Read returns '0' or '1' for read-write or read-only modes
  47 +               respectively.
  48 +               Write parses one of 'YyTt1NnFf0', or [oO][NnFf] for "on"
  49 +               and "off", i.e. what kstrbool() supports.
  50 +               Note: This file is only present if CONFIG_NVMEM_SYSFS
  51 +               is enabled.
  52 +
  53  What:          /sys/bus/nvmem/devices/.../nvmem
  54  Date:          July 2015
  55  KernelVersion:  4.2
  56 --- a/drivers/nvmem/core.c
  57 +++ b/drivers/nvmem/core.c
  58 @@ -185,7 +185,30 @@ static ssize_t type_show(struct device *
  59
  60  static DEVICE_ATTR_RO(type);
  61
  62 +static ssize_t force_ro_show(struct device *dev, struct device_attribute *attr,
  63 +                            char *buf)
  64 +{
  65 +       struct nvmem_device *nvmem = to_nvmem_device(dev);
  66 +
  67 +       return sysfs_emit(buf, "%d\n", nvmem->read_only);
  68 +}
  69 +
  70 +static ssize_t force_ro_store(struct device *dev, struct device_attribute *attr,
  71 +                             const char *buf, size_t count)
  72 +{
  73 +       struct nvmem_device *nvmem = to_nvmem_device(dev);
  74 +       int ret = kstrtobool(buf, &nvmem->read_only);
  75 +
  76 +       if (ret < 0)
  77 +               return ret;
  78 +
  79 +       return count;
  80 +}
  81 +
  82 +static DEVICE_ATTR_RW(force_ro);
  83 +
  84  static struct attribute *nvmem_attrs[] = {
  85 +       &dev_attr_force_ro.attr,
  86         &dev_attr_type.attr,
  87         NULL,
  88  };
  89 @@ -286,6 +309,25 @@ static umode_t nvmem_bin_attr_is_visible
  90         return nvmem_bin_attr_get_umode(nvmem);
  91  }
  92
  93 +static umode_t nvmem_attr_is_visible(struct kobject *kobj,
  94 +                                    struct attribute *attr, int i)
  95 +{
  96 +       struct device *dev = kobj_to_dev(kobj);
  97 +       struct nvmem_device *nvmem = to_nvmem_device(dev);
  98 +
  99 +       /*
 100 +        * If the device has no .reg_write operation, do not allow
 101 +        * configuration as read-write.
 102 +        * If the device is set as read-only by configuration, it
 103 +        * can be forced into read-write mode using the 'force_ro'
 104 +        * attribute.
 105 +        */
 106 +       if (attr == &dev_attr_force_ro.attr && !nvmem->reg_write)
 107 +               return 0;       /* Attribute not visible */
 108 +
 109 +       return attr->mode;
 110 +}
 111 +
 112  static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry,
 113                                             const char *id, int index);
 114
 115 @@ -342,6 +384,7 @@ static const struct attribute_group nvme
 116         .bin_attrs      = nvmem_bin_attributes,
 117         .attrs          = nvmem_attrs,
 118         .is_bin_visible = nvmem_bin_attr_is_visible,
 119 +       .is_visible     = nvmem_attr_is_visible,
 120  };
 121
 122  static const struct attribute_group *nvmem_dev_groups[] = {