mirror of https://github.com/acidanthera/audk.git
5e7c289fef
Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com> Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> |
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| .. | ||
| FdtPlatform.c | ||
| FdtPlatform.h | ||
| FdtPlatformDxe.inf | ||
| FdtPlatformDxe.uni | ||
| README.txt | ||
| ShellDumpFdt.c | ||
| ShellSetFdt.c | ||
README.txt
/** @file Copyright (c) 2015, ARM Ltd. All rights reserved.<BR> This program and the accompanying materials are licensed and made available under the terms and conditions of the BSD License which accompanies this distribution. The full text of the license may be found at http://opensource.org/licenses/bsd-license.php THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. **/ The purpose of the FdtPlatformDxe UEFI driver is to install the Flat Device Tree (FDT) of the platform the UEFI frimware is running on into the UEFI Configuration Table. The FDT is identified within the UEFI Configuration Table by the "gFdtTableGuid" GUID defined in "EmbeddedPkg.dec". Once installed, an UEFI application or OS boot loader can get from the UEFI Configuration Table the FDT of the platform from the "gFdtTableGuid" GUID. The installation is done after each boot at the end of the DXE phase, just before the BDS phase. It is done at the end of the DXE phase to be sure that all drivers have been dispatched. That way, all UEFI protocols that may be needed to retrieve the FDT can be made available. It is done before the BDS phase to be able to provide the FDT during that phase. The present driver tries to retrieve the FDT from the device paths defined in the "gEmbeddedTokenSpaceGuid.PcdFdtDevicePaths" PCD. The "PcdFdtDevicePaths" PCD contains a list a device paths. The device paths are in the text form and separated by semi-colons. The present driver tries the device paths in the order it finds them in the "PcdFdtDevicePaths" PCD as long as he did not install succesfully a FDT. The "PcdFdtDevicePaths" PCD is a dynamic PCD that can be modified during the DXE phase. This allows for exemple to select the right FDT when a binary is intended to run on several platforms and/or variants of a platform. If the driver manages to download a FDT from one of the device paths mentioned above then it installs it in the UEFI Configuration table and the run over the device paths is stopped. For development purposes only, if the feature PCD "gEmbeddedTokenSpaceGuid. PcdOverridePlatformFdt" is equal to TRUE, then before to try to install the FDT from the device paths listed in the "PcdFdtDevicePaths" PCD, the present driver tries to install it using the device path defined by the UEFI variable "Fdt". If the variable does not exist or the installation using the device path defined by the UEFI variable fails then the installation proceeds as described above. Furthermore and again for development purposes only, if the feature PCD "PcdOverridePlatformFdt" is equal to TRUE, the current driver provides the EFI Shell command "setfdt" to define the location of the FDT by the mean of an EFI Shell file path (like "fs2:\boot\fdt.dtb") or a device path. If the path passed in to the command is a valid EFI Shell file path, the command translates it into the corresponding device path and stores that device path in the "Fdt" UEFI variable asking for the variable to be non volatile. If the path passed in to the command is not recognised as a valid EFI Shell device path, the command handles it as device path and stored in the "Fdt" UEFI variable as it is. Finally, the "-i" option of the "setfdt" command allows to trigger the FDT installation process. The installation process is completed when the command returns. The command can be invoked with the "-i" option only and in that case the "Fdt" UEFI variable is not updated and the command just runs the FDT installation process. If the command is invoked with the "-i" option and an EFI Shell file path then first the "Fdt" UEFI variable is updated accordingly and then the FDT installation process is run.