firmware: coreboot: Add CFR firmware attributes driver

coreboot can publish a CFR tree in its coreboot table to describe
firmware setup options. Add a firmware-attributes driver for that table
entry under the coreboot firmware driver directory.

The driver exposes runtime EFI variable-backed boolean, enum and integer
settings through the firmware-attributes ABI. It only registers settings
with readable runtime EFI variables, skips suppressed, volatile,
dependency-gated and non-runtime options, and keeps read-only or inactive
options read-only in sysfs.

For settings with an APM_CNT runtime-apply record, write the EFI
variable and ask firmware to apply the setting immediately with an I/O
port SMI command. If firmware reports a failure, restore the old EFI
variable value. Settings without a runtime apply hook keep the EFI
variable update and set pending_reboot. Depend on HAS_IOPORT because
APM_CNT uses legacy I/O ports.

Tested on a Star Labs Byte with firmware 26.07: runtime APM_CNT apply
was verified with power_led, and reboot-needed behavior was verified with
debug_level.

Link: https://doc.coreboot.org/drivers/cfr.html
Link: https://doc.coreboot.org/drivers/cfr_internal.html
Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Link: https://lore.kernel.org/r/73204be94586622903da7fa90757fb091e8a7c2c.1788284852.git.sean@starlabs.systems
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

MAINTAINERS

@@ -6716,6 +6716,12 @@ F:	tools/testing/selftests/cgroup/test_hugetlb_memcg.c
 F:	tools/testing/selftests/cgroup/test_kmem.c
 F:	tools/testing/selftests/cgroup/test_memcontrol.c
 
+COREBOOT CFR FIRMWARE ATTRIBUTES DRIVER
+M:	Sean Rhodes <sean@starlabs.systems>
+L:	chrome-platform@lists.linux.dev
+S:	Maintained
+F:	drivers/firmware/coreboot/coreboot-cfr.c
+
 COREBOOT FIRMWARE DRIVERS
 M:	Tzung-Bi Shih <tzungbi@kernel.org>
 R:	Brian Norris <briannorris@chromium.org>

drivers/firmware/coreboot/Kconfig

@@ -49,6 +49,21 @@ config COREBOOT_TABLE
 	  device tree node /firmware/coreboot.
 	  If unsure say N.
 
+config COREBOOT_CFR
+	tristate "coreboot CFR firmware attributes"
+	depends on EFI
+	depends on COREBOOT_TABLE
+	depends on HAS_IOPORT
+	select CRC32
+	select FW_ATTR_CLASS
+	help
+	  This driver parses the coreboot CFR table and exposes runtime EFI
+	  variable-backed options through the firmware-attributes sysfs
+	  interface.
+
+	  If you have a system running coreboot with CFR runtime
+	  configuration support, say Y or M here.
+
 config COREBOOT_MEMCONSOLE_COMMON
 	tristate
 	depends on GOOGLE_MEMCONSOLE_X86_LEGACY || COREBOOT_MEMCONSOLE

drivers/firmware/coreboot/Makefile

@@ -2,6 +2,7 @@
 
 obj-$(CONFIG_GOOGLE_SMI)		+= gsmi.o
 obj-$(CONFIG_COREBOOT_TABLE)               += coreboot_table.o
+obj-$(CONFIG_COREBOOT_CFR)		+= coreboot-cfr.o
 obj-$(CONFIG_COREBOOT_FRAMEBUFFER)         += framebuffer-coreboot.o
 obj-$(CONFIG_COREBOOT_MEMCONSOLE_COMMON)   += memconsole.o
 obj-$(CONFIG_COREBOOT_MEMCONSOLE)          += memconsole-coreboot.o