xref: /openbmc/linux/Documentation/ABI/testing/sysfs-bus-coreboot (revision ebab9426)

What:		/sys/bus/coreboot
Date:		August 2022
Contact:	Jack Rosenthal <jrosenth@chromium.org>
Description:
		The coreboot bus provides a variety of virtual devices used to
		access data structures created by the Coreboot BIOS.

What:		/sys/bus/coreboot/devices/cbmem-<id>
Date:		August 2022
Contact:	Jack Rosenthal <jrosenth@chromium.org>
Description:
		CBMEM is a downwards-growing memory region created by Coreboot,
		and contains tagged data structures to be shared with payloads
		in the boot process and the OS.  Each CBMEM entry is given a
		directory in /sys/bus/coreboot/devices based on its id.
		A list of ids known to Coreboot can be found in the coreboot
		source tree at
		``src/commonlib/bsd/include/commonlib/bsd/cbmem_id.h``.

What:		/sys/bus/coreboot/devices/cbmem-<id>/address
Date:		August 2022
Contact:	Jack Rosenthal <jrosenth@chromium.org>
Description:
		This is the physical memory address that the CBMEM entry's data
		begins at, in hexadecimal (e.g., ``0x76ffe000``).

What:		/sys/bus/coreboot/devices/cbmem-<id>/size
Date:		August 2022
Contact:	Jack Rosenthal <jrosenth@chromium.org>
Description:
		This is the size of the CBMEM entry's data, in hexadecimal
		(e.g., ``0x1234``).

What:		/sys/bus/coreboot/devices/cbmem-<id>/mem
Date:		August 2022
Contact:	Jack Rosenthal <jrosenth@chromium.org>
Description:
		A file exposing read/write access to the entry's data.  Note
		that this file does not support mmap(), as coreboot
		does not guarantee that the data will be page-aligned.

		The mode of this file is 0600.  While there shouldn't be
		anything security-sensitive contained in CBMEM, read access
		requires root privileges given this is exposing a small subset
		of physical memory.