1/** @file 2 3 Copyright (c) 2015, ARM Ltd. All rights reserved.<BR> 4 5 This program and the accompanying materials 6 are licensed and made available under the terms and conditions of the BSD License 7 which accompanies this distribution. The full text of the license may be found at 8 http://opensource.org/licenses/bsd-license.php 9 10 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, 11 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. 12 13**/ 14 15The purpose of the FdtPlatformDxe UEFI driver is to install the Flat Device 16Tree (FDT) of the platform the UEFI frimware is running on into the UEFI 17Configuration Table. The FDT is identified within the UEFI Configuration 18Table by the "gFdtTableGuid" GUID defined in "EmbeddedPkg.dec". 19 20Once installed, an UEFI application or OS boot loader can get from the UEFI 21Configuration Table the FDT of the platform from the "gFdtTableGuid" GUID. 22 23The installation is done after each boot at the end of the DXE phase, 24just before the BDS phase. It is done at the end of the DXE phase to be sure 25that all drivers have been dispatched. That way, all UEFI protocols that may 26be needed to retrieve the FDT can be made available. It is done before the BDS 27phase to be able to provide the FDT during that phase. 28 29The present driver tries to retrieve the FDT from the device paths defined in the 30"gEmbeddedTokenSpaceGuid.PcdFdtDevicePaths" PCD. The "PcdFdtDevicePaths" PCD 31contains a list a device paths. The device paths are in the text form and 32separated by semi-colons. The present driver tries the device paths in the order 33it finds them in the "PcdFdtDevicePaths" PCD as long as he did not install 34succesfully a FDT. 35 36The "PcdFdtDevicePaths" PCD is a dynamic PCD that can be modified during the 37DXE phase. This allows for exemple to select the right FDT when a binary is 38intended to run on several platforms and/or variants of a platform. 39 40If the driver manages to download a FDT from one of the device paths mentioned 41above then it installs it in the UEFI Configuration table and the run over the 42device paths is stopped. 43 44For development purposes only, if the feature PCD "gEmbeddedTokenSpaceGuid. 45PcdOverridePlatformFdt" is equal to TRUE, then before to try to install the 46FDT from the device paths listed in the "PcdFdtDevicePaths" PCD, the present 47driver tries to install it using the device path defined by the UEFI variable 48"Fdt". If the variable does not exist or the installation using the device path 49defined by the UEFI variable fails then the installation proceeds as described 50above. 51 52Furthermore and again for development purposes only, if the feature PCD 53"PcdOverridePlatformFdt" is equal to TRUE, the current driver provides the EFI 54Shell command "setfdt" to define the location of the FDT by the mean of an EFI 55Shell file path (like "fs2:\boot\fdt.dtb") or a device path. 56 57If the path passed in to the command is a valid EFI Shell file path, the 58command translates it into the corresponding device path and stores that 59device path in the "Fdt" UEFI variable asking for the variable to be non 60volatile. 61 62If the path passed in to the command is not recognised as a valid EFI 63Shell device path, the command handles it as device path and stored 64in the "Fdt" UEFI variable as it is. 65 66Finally, the "-i" option of the "setfdt" command allows to trigger the FDT 67installation process. The installation process is completed when the command 68returns. The command can be invoked with the "-i" option only and in that 69case the "Fdt" UEFI variable is not updated and the command just runs the 70FDT installation process. If the command is invoked with the "-i" option and 71an EFI Shell file path then first the "Fdt" UEFI variable is updated accordingly 72and then the FDT installation process is run. 73