xref: /linux/Documentation/ABI/testing/sysfs-class-firmware-attributes (revision 5b09081f4c5c7159cb3789f35bb82bd9d32061c9)

What:		/sys/class/firmware-attributes/*/attributes/*/
Date:		February 2021
KernelVersion:	5.11
Contact:	Divya Bharathi <Divya.Bharathi@Dell.com>,
		Mario Limonciello <mario.limonciello@dell.com>,
		Prasanth KSR <prasanth.ksr@dell.com>
Description:
		A sysfs interface for systems management software to enable
		configuration capability on supported systems.  This directory
		exposes interfaces for interacting with configuration options.

		Unless otherwise specified in an attribute description all attributes are optional
		and will accept UTF-8 input.

		type:
		    A file that can be read to obtain the type of attribute.
		    This attribute is mandatory.

		The following are known types:

			- enumeration: a set of pre-defined valid values
			- integer: a range of numerical values
			- string

		All attribute types support the following values:

		current_value:
				A file that can be read to obtain the current
				value of the <attr>.

				This file can also be written to in order to update the value of a
				<attr>

				This attribute is mandatory.

		default_value:
				A file that can be read to obtain the default
				value of the <attr>

		display_name:
				A file that can be read to obtain a user friendly
				description of the at <attr>

		display_name_language_code:
						A file that can be read to obtain
						the IETF language tag corresponding to the
						"display_name" of the <attr>

		"enumeration"-type specific properties:

		possible_values:
					A file that can be read to obtain the possible
					values of the <attr>. Values are separated using
					semi-colon (``;``).

		"integer"-type specific properties:

		min_value:
				A file that can be read to obtain the lower
				bound value of the <attr>

		max_value:
				A file that can be read to obtain the upper
				bound value of the <attr>

		scalar_increment:
					A file that can be read to obtain the scalar value used for
					increments of current_value this attribute accepts.

		"string"-type specific properties:

		max_length:
				A file that can be read to obtain the maximum
				length value of the <attr>

		min_length:
				A file that can be read to obtain the minimum
				length value of the <attr>

		Dell specific class extensions
		------------------------------

		On Dell systems the following additional attributes are available:

		dell_modifier:
				A file that can be read to obtain attribute-level
				dependency rule. It says an attribute X will become read-only or
				suppressed, if/if-not attribute Y is configured.

				modifier rules can be in following format::

				    [ReadOnlyIf:<attribute>=<value>]
				    [ReadOnlyIfNot:<attribute>=<value>]
				    [SuppressIf:<attribute>=<value>]
				    [SuppressIfNot:<attribute>=<value>]

				For example::

				    AutoOnFri/dell_modifier has value,
					    [SuppressIfNot:AutoOn=SelectDays]

				This means AutoOnFri will be suppressed in BIOS setup if AutoOn
				attribute is not "SelectDays" and its value will not be effective
				through sysfs until this rule is met.

		Enumeration attributes also support the following:

		dell_value_modifier:
					A file that can be read to obtain value-level dependency.
					This file is similar to dell_modifier but here,	an
					attribute's current value will be forcefully changed based
					dependent attributes value.

					dell_value_modifier rules can be in following format::

					    <value>[ForceIf:<attribute>=<value>]
					    <value>[ForceIfNot:<attribute>=<value>]

					For example:

					    LegacyOrom/dell_value_modifier has value:
						    Disabled[ForceIf:SecureBoot=Enabled]

					This means LegacyOrom's current value will be forced to
					"Disabled" in BIOS setup if SecureBoot is Enabled and its
					value will not be effective through sysfs until this rule is
					met.

What:		/sys/class/firmware-attributes/*/authentication/
Date:		February 2021
KernelVersion:	5.11
Contact:	Divya Bharathi <Divya.Bharathi@Dell.com>,
		Mario Limonciello <mario.limonciello@dell.com>,
		Prasanth KSR <prasanth.ksr@dell.com>
Description:
		Devices support various authentication mechanisms which can be exposed
		as a separate configuration object.

		For example a "BIOS Admin" password and "System" Password can be set,
		reset or cleared using these attributes.

		- An "Admin" password is used for preventing modification to the BIOS
		  settings.
		- A "System" password is required to boot a machine.

		Change in any of these two authentication methods will also generate an
		uevent KOBJ_CHANGE.

		is_enabled:
					A file that can be read to obtain a 0/1 flag to see if
					<attr> authentication is enabled.
					This attribute is mandatory.

		role:
					The type of authentication used.
					This attribute is mandatory.

					Known types:
						bios-admin:
							Representing BIOS administrator password
						power-on:
							Representing a password required to use
							the system

		mechanism:
					The means of authentication.  This attribute is mandatory.
					Only supported type currently is "password".

		max_password_length:
					A file that can be read to obtain the
					maximum length of the Password

		min_password_length:
					A file that can be read to obtain the
					minimum length of the Password

		current_password:
					A write only value used for privileged access such as
					setting	attributes when a system or admin password is set
					or resetting to a new password

					This attribute is mandatory when mechanism == "password".

		new_password:
					A write only value that when used in tandem with
					current_password will reset a system or admin password.

		Note, password management is session specific. If Admin password is set,
		same password must be written into current_password file (required for
		password-validation) and must be cleared once the session is over.
		For example::

			echo "password" > current_password
			echo "disabled" > TouchScreen/current_value
			echo "" > current_password

		Drivers may emit a CHANGE uevent when a password is set or unset
		userspace may check it again.

		On Dell systems, if Admin password is set, then all BIOS attributes
		require password validation.

What:		/sys/class/firmware-attributes/*/attributes/pending_reboot
Date:		February 2021
KernelVersion:	5.11
Contact:	Divya Bharathi <Divya.Bharathi@Dell.com>,
		Mario Limonciello <mario.limonciello@dell.com>,
		Prasanth KSR <prasanth.ksr@dell.com>
Description:
		A read-only attribute reads 1 if a reboot is necessary to apply
		pending BIOS attribute changes. Also, an uevent_KOBJ_CHANGE is
		generated when it changes to 1.

			==	=========================================
			0	All BIOS attributes setting are current
			1	A reboot is necessary to get pending BIOS
			        attribute changes applied
			==	=========================================

		Note, userspace applications need to follow below steps for efficient
		BIOS management,

		1.	Check if admin password is set. If yes, follow session method for
			password management as briefed under authentication section above.
		2.	Before setting any attribute, check if it has any modifiers
			or value_modifiers. If yes, incorporate them and then modify
			attribute.

		Drivers may emit a CHANGE uevent when this value changes and userspace
		may check it again.

What:		/sys/class/firmware-attributes/*/attributes/reset_bios
Date:		February 2021
KernelVersion:	5.11
Contact:	Divya Bharathi <Divya.Bharathi@Dell.com>,
		Mario Limonciello <mario.limonciello@dell.com>,
		Prasanth KSR <prasanth.ksr@dell.com>
Description:
		This attribute can be used to reset the BIOS Configuration.
		Specifically, it tells which type of reset BIOS configuration is being
		requested on the host.

		Reading from it returns a list of supported options encoded as:

			- 'builtinsafe' (Built in safe configuration profile)
			- 'lastknowngood' (Last known good saved configuration profile)
			- 'factory' (Default factory settings configuration profile)
			- 'custom' (Custom saved configuration profile)

		The currently selected option is printed in square brackets as
		shown below::

		    # echo "factory" > /sys/class/firmware-attributes/*/device/attributes/reset_bios
		    # cat /sys/class/firmware-attributes/*/device/attributes/reset_bios
		    # builtinsafe lastknowngood [factory] custom

		Note that any changes to this attribute requires a reboot
		for changes to take effect.