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diff --git a/doc/uefi/uefi.rst b/doc/uefi/uefi.rst new file mode 100644 index 0000000000..db942df694 --- /dev/null +++ b/doc/uefi/uefi.rst @@ -0,0 +1,334 @@ +.. SPDX-License-Identifier: GPL-2.0+ +.. Copyright (c) 2018 Heinrich Schuchardt + +UEFI on U-Boot +============== + +The Unified Extensible Firmware Interface Specification (UEFI) [1] has become +the default for booting on AArch64 and x86 systems. It provides a stable API for +the interaction of drivers and applications with the firmware. The API comprises +access to block storage, network, and console to name a few. The Linux kernel +and boot loaders like GRUB or the FreeBSD loader can be executed. + +Development target +------------------ + +The implementation of UEFI in U-Boot strives to reach the requirements described +in the "Embedded Base Boot Requirements (EBBR) Specification - Release v1.0" +[2]. The "Server Base Boot Requirements System Software on ARM Platforms" [3] +describes a superset of the EBBR specification and may be used as further +reference. + +A full blown UEFI implementation would contradict the U-Boot design principle +"keep it small". + +Building U-Boot for UEFI +------------------------ + +The UEFI standard supports only little-endian systems. The UEFI support can be +activated for ARM and x86 by specifying:: + + CONFIG_CMD_BOOTEFI=y + CONFIG_EFI_LOADER=y + +in the .config file. + +Support for attaching virtual block devices, e.g. iSCSI drives connected by the +loaded UEFI application [4], requires:: + + CONFIG_BLK=y + CONFIG_PARTITIONS=y + +Executing a UEFI binary +~~~~~~~~~~~~~~~~~~~~~~~ + +The bootefi command is used to start UEFI applications or to install UEFI +drivers. It takes two parameters:: + + bootefi <image address> [fdt address] + +* image address - the memory address of the UEFI binary +* fdt address - the memory address of the flattened device tree + +Below you find the output of an example session starting GRUB:: + + => load mmc 0:2 ${fdt_addr_r} boot/dtb + 29830 bytes read in 14 ms (2 MiB/s) + => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi + reading efi/debian/grubaa64.efi + 120832 bytes read in 7 ms (16.5 MiB/s) + => bootefi ${kernel_addr_r} ${fdt_addr_r} + +The environment variable 'bootargs' is passed as load options in the UEFI system +table. The Linux kernel EFI stub uses the load options as command line +arguments. + +Executing the boot manager +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The UEFI specification foresees to define boot entries and boot sequence via UEFI +variables. Booting according to these variables is possible via:: + + bootefi bootmgr [fdt address] + +As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at +runtime. + +Executing the built in hello world application +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A hello world UEFI application can be built with:: + + CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y + +It can be embedded into the U-Boot binary with:: + + CONFIG_CMD_BOOTEFI_HELLO=y + +The bootefi command is used to start the embedded hello world application:: + + bootefi hello [fdt address] + +Below you find the output of an example session:: + + => bootefi hello ${fdtcontroladdr} + ## Starting EFI application at 01000000 ... + WARNING: using memory device/image path, this may confuse some payloads! + Hello, world! + Running on UEFI 2.7 + Have SMBIOS table + Have device tree + Load options: root=/dev/sdb3 init=/sbin/init rootwait ro + ## Application terminated, r = 0 + +The environment variable fdtcontroladdr points to U-Boot's internal device tree +(if available). + +Executing the built-in self-test +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +An UEFI self-test suite can be embedded in U-Boot by building with:: + + CONFIG_CMD_BOOTEFI_SELFTEST=y + +For testing the UEFI implementation the bootefi command can be used to start the +self-test:: + + bootefi selftest [fdt address] + +The environment variable 'efi_selftest' can be used to select a single test. If +it is not provided all tests are executed except those marked as 'on request'. +If the environment variable is set to 'list' a list of all tests is shown. + +Below you can find the output of an example session:: + + => setenv efi_selftest simple network protocol + => bootefi selftest + Testing EFI API implementation + Selected test: 'simple network protocol' + Setting up 'simple network protocol' + Setting up 'simple network protocol' succeeded + Executing 'simple network protocol' + DHCP Discover + DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02) + as broadcast message. + Executing 'simple network protocol' succeeded + Tearing down 'simple network protocol' + Tearing down 'simple network protocol' succeeded + Boot services terminated + Summary: 0 failures + Preparing for reset. Press any key. + +The UEFI life cycle +------------------- + +After the U-Boot platform has been initialized the UEFI API provides two kinds +of services: + +* boot services +* runtime services + +The API can be extended by loading UEFI drivers which come in two variants: + +* boot drivers +* runtime drivers + +UEFI drivers are installed with U-Boot's bootefi command. With the same command +UEFI applications can be executed. + +Loaded images of UEFI drivers stay in memory after returning to U-Boot while +loaded images of applications are removed from memory. + +An UEFI application (e.g. an operating system) that wants to take full control +of the system calls ExitBootServices. After a UEFI application calls +ExitBootServices + +* boot services are not available anymore +* timer events are stopped +* the memory used by U-Boot except for runtime services is released +* the memory used by boot time drivers is released + +So this is a point of no return. Afterwards the UEFI application can only return +to U-Boot by rebooting. + +The UEFI object model +--------------------- + +UEFI offers a flexible and expandable object model. The objects in the UEFI API +are devices, drivers, and loaded images. These objects are referenced by +handles. + +The interfaces implemented by the objects are referred to as protocols. These +are identified by GUIDs. They can be installed and uninstalled by calling the +appropriate boot services. + +Handles are created by the InstallProtocolInterface or the +InstallMultipleProtocolinterfaces service if NULL is passed as handle. + +Handles are deleted when the last protocol has been removed with the +UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service. + +Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation +of device nodes. By their device paths all devices of a system are arranged in a +tree. + +Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect +a driver to devices (which are referenced as controllers in this context). + +Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta +information about the image and a pointer to the unload callback function. + +The UEFI events +--------------- + +In the UEFI terminology an event is a data object referencing a notification +function which is queued for calling when the event is signaled. The following +types of events exist: + +* periodic and single shot timer events +* exit boot services events, triggered by calling the ExitBootServices() service +* virtual address change events +* memory map change events +* read to boot events +* reset system events +* system table events +* events that are only triggered programmatically + +Events can be created with the CreateEvent service and deleted with CloseEvent +service. + +Events can be assigned to an event group. If any of the events in a group is +signaled, all other events in the group are also set to the signaled state. + +The UEFI driver model +--------------------- + +A driver is specific for a single protocol installed on a device. To install a +driver on a device the ConnectController service is called. In this context +controller refers to the device for which the driver is installed. + +The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This +protocol has has three functions: + +* supported - determines if the driver is compatible with the device +* start - installs the driver by opening the relevant protocol with + attribute EFI_OPEN_PROTOCOL_BY_DRIVER +* stop - uninstalls the driver + +The driver may create child controllers (child devices). E.g. a driver for block +IO devices will create the device handles for the partitions. The child +controllers will open the supported protocol with the attribute +EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER. + +A driver can be detached from a device using the DisconnectController service. + +U-Boot devices mapped as UEFI devices +------------------------------------- + +Some of the U-Boot devices are mapped as UEFI devices + +* block IO devices +* console +* graphical output +* network adapter + +As of U-Boot 2018.03 the logic for doing this is hard coded. + +The development target is to integrate the setup of these UEFI devices with the +U-Boot driver model [5]. So when a U-Boot device is discovered a handle should +be created and the device path protocol and the relevant IO protocol should be +installed. The UEFI driver then would be attached by calling ConnectController. +When a U-Boot device is removed DisconnectController should be called. + +UEFI devices mapped as U-Boot devices +------------------------------------- + +UEFI drivers binaries and applications may create new (virtual) devices, install +a protocol and call the ConnectController service. Now the matching UEFI driver +is determined by iterating over the implementations of the +EFI_DRIVER_BINDING_PROTOCOL. + +It is the task of the UEFI driver to create a corresponding U-Boot device and to +proxy calls for this U-Boot device to the controller. + +In U-Boot 2018.03 this has only been implemented for block IO devices. + +UEFI uclass +~~~~~~~~~~~ + +An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that +takes care of initializing the UEFI drivers and providing the +EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers. + +A linker created list is used to keep track of the UEFI drivers. To create an +entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying +UCLASS_EFI as the ID of its uclass, e.g:: + + /* Identify as UEFI driver */ + U_BOOT_DRIVER(efi_block) = { + .name = "EFI block driver", + .id = UCLASS_EFI, + .ops = &driver_ops, + }; + +The available operations are defined via the structure struct efi_driver_ops:: + + struct efi_driver_ops { + const efi_guid_t *protocol; + const efi_guid_t *child_protocol; + int (*bind)(efi_handle_t handle, void *interface); + }; + +When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the +uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver. +In the start() function the bind() function of the UEFI driver is called after +checking the GUID. +The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child +controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03 +this is not yet completely implemented.) + +UEFI block IO driver +~~~~~~~~~~~~~~~~~~~~ + +The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL. + +When connected it creates a new U-Boot block IO device with interface type +IF_TYPE_EFI, adds child controllers mapping the partitions, and installs the +EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the +software iPXE to boot from iSCSI network drives [4]. + +This driver is only available if U-Boot is configured with:: + + CONFIG_BLK=y + CONFIG_PARTITIONS=y + +Links +----- + +* [1] http://uefi.org/specifications - UEFI specifications +* [2] https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf - + Embedded Base Boot Requirements (EBBR) Specification - Release v1.0 +* [3] https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-system-software-on-arm-platforms-version-11 - + Server Base Boot Requirements System Software on ARM Platforms - Version 1.1 +* [4] :doc:`iscsi` +* [5] :doc:`../driver-model/index` |