Commit 9d7eb234 authored by Marek Vasut's avatar Marek Vasut Committed by Greg Kroah-Hartman
Browse files

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: default avatarMarek Vasut <marex@denx.de>
Signed-off-by: default avatarSrinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20240705074852.423202-16-srinivas.kandagatla@linaro.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 08c367e4

Documentation/ABI/stable/sysfs-bus-nvmem

+17 −0
Original line number Diff line number Diff line 
What:		/sys/bus/nvmem/devices/.../force_ro

Date:		June 2024

KernelVersion:	6.11

Contact:	Marek Vasut <marex@denx.de>

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

drivers/nvmem/core.c

+43 −0
Original line number Diff line number Diff line
@@ -184,7 +184,30 @@ static ssize_t type_show(struct device *dev, 


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(struct kobject *kobj, 
	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 nvmem_bin_group = { 
	.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[] = {