From 9d7eb234ac7a56b88aea8a52ed81553a730fe25c Mon Sep 17 00:00:00 2001 From: Marek Vasut Date: Fri, 5 Jul 2024 08:48:52 +0100 Subject: [PATCH] nvmem: core: Implement force_ro sysfs attribute Implement "force_ro" sysfs attribute to allow users to set read-write devices as read-only and back to read-write from userspace. The choice of the name is based on MMC core 'force_ro' attribute. This solves a situation where an AT24 I2C EEPROM with GPIO based nWP signal may have to be occasionally updated. Such I2C EEPROM device is usually set as read-only during most of the regular system operation, but in case it has to be updated in a controlled manner, it could be unlocked using this new "force_ro" sysfs attribute and then re-locked again. The "read-only" DT property and config->read_only configuration is respected and is used to set default state of the device, read-only or read-write, for devices which do implement .reg_write function. For devices which do not implement .reg_write function, the device is unconditionally read-only and the "force_ro" attribute is not visible. Signed-off-by: Marek Vasut Signed-off-by: Srinivas Kandagatla Link: https://lore.kernel.org/r/20240705074852.423202-16-srinivas.kandagatla@linaro.org Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/stable/sysfs-bus-nvmem | 17 ++++++++++ drivers/nvmem/core.c | 43 ++++++++++++++++++++++++ 2 files changed, 60 insertions(+) --- a/Documentation/ABI/stable/sysfs-bus-nvmem +++ b/Documentation/ABI/stable/sysfs-bus-nvmem @@ -1,3 +1,20 @@ +What: /sys/bus/nvmem/devices/.../force_ro +Date: June 2024 +KernelVersion: 6.11 +Contact: Marek Vasut +Description: + This read/write attribute allows users to set read-write + devices as read-only and back to read-write from userspace. + This can be used to unlock and relock write-protection of + devices which are generally locked, except during sporadic + programming operation. + Read returns '0' or '1' for read-write or read-only modes + respectively. + Write parses one of 'YyTt1NnFf0', or [oO][NnFf] for "on" + and "off", i.e. what kstrbool() supports. + Note: This file is only present if CONFIG_NVMEM_SYSFS + is enabled. + What: /sys/bus/nvmem/devices/.../nvmem Date: July 2015 KernelVersion: 4.2 --- a/drivers/nvmem/core.c +++ b/drivers/nvmem/core.c @@ -184,7 +184,30 @@ static ssize_t type_show(struct device * static DEVICE_ATTR_RO(type); +static ssize_t force_ro_show(struct device *dev, struct device_attribute *attr, + char *buf) +{ + struct nvmem_device *nvmem = to_nvmem_device(dev); + + return sysfs_emit(buf, "%d\n", nvmem->read_only); +} + +static ssize_t force_ro_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct nvmem_device *nvmem = to_nvmem_device(dev); + int ret = kstrtobool(buf, &nvmem->read_only); + + if (ret < 0) + return ret; + + return count; +} + +static DEVICE_ATTR_RW(force_ro); + static struct attribute *nvmem_attrs[] = { + &dev_attr_force_ro.attr, &dev_attr_type.attr, NULL, }; @@ -285,6 +308,25 @@ static umode_t nvmem_bin_attr_is_visible return nvmem_bin_attr_get_umode(nvmem); } +static umode_t nvmem_attr_is_visible(struct kobject *kobj, + struct attribute *attr, int i) +{ + struct device *dev = kobj_to_dev(kobj); + struct nvmem_device *nvmem = to_nvmem_device(dev); + + /* + * If the device has no .reg_write operation, do not allow + * configuration as read-write. + * If the device is set as read-only by configuration, it + * can be forced into read-write mode using the 'force_ro' + * attribute. + */ + if (attr == &dev_attr_force_ro.attr && !nvmem->reg_write) + return 0; /* Attribute not visible */ + + return attr->mode; +} + static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry, const char *id, int index); @@ -341,6 +383,7 @@ static const struct attribute_group nvme .bin_attrs = nvmem_bin_attributes, .attrs = nvmem_attrs, .is_bin_visible = nvmem_bin_attr_is_visible, + .is_visible = nvmem_attr_is_visible, }; static const struct attribute_group *nvmem_dev_groups[] = {