ACPI: Introduce Platform Firmware Runtime Update device driver

Introduce the pfr_update driver which can be used for Platform Firmware
Runtime code injection and driver update [1].

The user is expected to provide the EFI capsule, and pass it to the
driver by writing the capsule to a device special file. The capsule
is transferred by the driver to the platform firmware with the help
of an ACPI _DSM method under the special ACPI Platform Firmware
Runtime Update device (INTC1080), and the actual firmware update is
carried out by the low-level Management Mode code in the platform
firmware.

This change allows certain pieces of the platform firmware to be
updated on the fly while the system is running (runtime) without the
need to restart it, which is key in the cases when the system needs to
be available 100% of the time and it cannot afford the downtime related
to restarting it, or when the work carried out by the system is
particularly important, so it cannot be interrupted, and it is not
practical to wait until it is complete.

Link: https://uefi.org/sites/default/files/resources/Intel_MM_OS_Interface_Spec_Rev100.pdf # [1]
Tested-by: Hongyu Ning <hongyu.ning@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/userspace-api/ioctl/ioctl-number.rst

@@ -367,6 +367,7 @@ Code  Seq#    Include File                                           Comments
                                                                      <mailto:aherrman@de.ibm.com>
 0xE5  00-3F  linux/fuse.h
 0xEC  00-01  drivers/platform/chrome/cros_ec_dev.h                   ChromeOS EC driver
+0xEE  00-09  uapi/linux/pfrut.h                                      Platform Firmware Runtime Update and Telemetry
 0xF3  00-3F  drivers/usb/misc/sisusbvga/sisusb.h                     sisfb (in development)
                                                                      <mailto:thomas@winischhofer.net>
 0xF6  all                                                            LTTng Linux Trace Toolkit Next Generation

drivers/acpi/Kconfig

@@ -517,6 +517,24 @@ config ACPI_CONFIGFS
 	  userspace. The configurable ACPI groups will be visible under
 	  /config/acpi, assuming configfs is mounted under /config.
 
+config ACPI_PFRUT
+	tristate "ACPI Platform Firmware Runtime Update and Telemetry"
+	depends on 64BIT
+	help
+	  This mechanism allows certain pieces of the platform firmware
+	  to be updated on the fly while the system is running (runtime)
+	  without the need to restart it, which is key in the cases when
+	  the system needs to be available 100% of the time and it cannot
+	  afford the downtime related to restarting it, or when the work
+	  carried out by the system is particularly important, so it cannot
+	  be interrupted, and it is not practical to wait until it is complete.
+
+	  The existing firmware code can be modified (driver update) or
+	  extended by adding new code to the firmware (code injection).
+
+	  To compile this driver as module, choose M here:
+	  the module will be called pfr_update.
+
 if ARM64
 source "drivers/acpi/arm64/Kconfig"
 

drivers/acpi/Makefile

@@ -102,6 +102,7 @@ obj-$(CONFIG_ACPI_CPPC_LIB)	+= cppc_acpi.o
 obj-$(CONFIG_ACPI_SPCR_TABLE)	+= spcr.o
 obj-$(CONFIG_ACPI_DEBUGGER_USER) += acpi_dbg.o
 obj-$(CONFIG_ACPI_PPTT) 	+= pptt.o
+obj-$(CONFIG_ACPI_PFRUT)	+= pfr_update.o
 
 # processor has its own "processor." module_param namespace
 processor-y			:= processor_driver.o