11.6. Device Tree Support

Important

For any information about Device Trees refer to the QNX J721E BSP user guide accessable via QNX Software Center for further details. If there are still questions contact QNX for any questions about Device Tree.

11.6.1. Introduction

Starting in QNX SDP 8.0, Device Trees (DTs) are required for io-sock based networking. At the time of writing the Device Tree Blobs (DTBs) must be loaded into memory by the bootloader prior to the QNX image taking over.

Support for loading DTBs has been added to Processor SDK J721E QNX for the following boot modes:

  1. U-boot

  2. SBL+BootApp

  3. SBL Combined Boot

Note

The configurations for each SOC have been updated with defaults based on the BSP revision they were validated with. If running on a TI EVM with the same BSP revision, then no modifications should be required. If using a custom board contact QNX for DTB related support. PSDK QNX does not own the DTB being used and is distributed via the QNX BSP!!!

  • In U-boot, the DTB is stored in the bootfs partition of the SD card. The U-boot boot script (uEnv.txt) then loads the specified DTB to the specified memory address before jumping to the QNX image.

  • In SBL with BootApp, the DTB is linked into the QNX appimage. This is different than Linux whose DTB is stored as another appimage along side the Linux appimage.

  • In SBL Combined Boot, the DTB is built into the combined appimage via the standard SBL build flow.

Follow the below instructions for adding/customizing the loading of DTBs.

11.6.2. Instructions for Loading Customer Device Trees in PSDK QNX

11.6.2.1. Modifications Required for Both U-boot and SBL

These configurations are required for both U-boot and SBL. The majority of the DTB configuration happens in ${PSDK_QNX_PATH}/soc_config.mk. An excerpt of this file is shown below:

############################
## Device Tree Configuration
############################
# Define FDT_PATH, FDT_BIN_NAME, and FDT_LOAD_ADDR for each given SOC.
# If not defined then no FDT will be copied/built into Uboot or SBL.
ifeq ($(SOC), j721e)

  ifeq ($(QNX_SDP_VERSION), 800)
    FDT_PATH=$(PSDK_QNX_PATH)/qnx/bsp/prebuilt/usr/lib/
    FDT_BIN_NAME=psdk_linux_9.2_k3-j721e-common-proc-board-quad-port-eth-exp.dtb
    FDT_LOAD_ADDR=0x88000000
  endif

else ifeq ($(SOC), j721s2)

  ifeq ($(QNX_SDP_VERSION), 800)
    FDT_PATH=$(PSDK_QNX_PATH)/qnx/bsp/prebuilt/usr/lib
    FDT_BIN_NAME=psdk_linux_9.2_k3-j721s2-common-proc-board.dtb
    FDT_LOAD_ADDR=0x88000000
  endif

else ifeq ($(SOC), j784s4)

  ifeq ($(QNX_SDP_VERSION), 800)
    FDT_PATH=$(PSDK_QNX_PATH)/qnx/bsp/prebuilt/usr/lib
    #FDT_BIN_NAME=psdk_linux_9.2_k3-j784s4-evm.dtb
    FDT_BIN_NAME=psdk_linux_9.2_k3-j784s4-evm-quad-port-eth-exp1.dtb
    FDT_LOAD_ADDR=0x88000000
  endif

else ifeq ($(SOC), j722s)

  ifeq ($(QNX_SDP_VERSION), 800)
    FDT_PATH=$(PSDK_QNX_PATH)/qnx/bsp/prebuilt/usr/lib
    FDT_BIN_NAME=psdk_linux_9.2_k3-j722s-evm.dtb
    FDT_LOAD_ADDR=0x88000000
  endif

endif

The purpose of this code section is to define the 3 make flags FDT_PATH, FDT_BIN_NAME, and FDT_LOAD_ADDR when a Device Tree is desired to be loaded. At the time of writing DTBs are only required when running on a SDP 8.0 platform with io-sock base networking so these make flags are only defined under SDP 8.0. Consequently, in the PSDK QNX default soc_config.mk, these flags are only active under SDP 8.0.

To modify which DTB is loaded by the PSDK QNX make system, update the above flags accordingly.

FDT_BIN_NAME is the flag that is checked before modifying the build process. This means that if FDT_BIN_NAME is defined, then the other two flags must be defined or build errors will occur.

11.6.2.2. Modifications Required for U-boot Only

The U-boot uEnv.txt boot script needs to be updated with the load address and name of the dtb file. An excerpt of default U-boot script, at the time of writing, is shown below:

# This uEnv.txt file can contain additional environment settings that you
# want to set in U-Boot at boot time.  This can be simple variables such
# as the serverip or custom variables.  The format of this file is:
#    variable=value
# NOTE: This file will be evaluated after the bootcmd is run and the
#       bootcmd must be set to load this file if it exists (this is the
#       default on all newer U-Boot images.  This also means that some
#       variables such as bootdelay cannot be changed by this file since
#       it is not evaluated until the bootcmd is run.

dtb_name=psdk_linux_9.2_k3-j784s4-evm-quad-port-eth-exp1.dtb
ifs_load_addr=0x80080000
dtb_load_addr=0x88000000
dorprocboot=1

In the uEnv.txt file the variables dtb_name and dtb_load_addr must be populated. In the case of J721E, the U-boot script to update is ${PSDK_QNX_PATH}/qnx/scripts/u-boot/uEnv_ j721e.txt.

11.6.2.3. Modifications Required for SBL with Bootapp Only

As mentioned earlier, the DTB is built into the QNX appimage in the case of SBL with bootapp. If you need to use a DTB address that is different than the default, then the QNX appimage linker script needs to be updated: ${PSDK_QNX_PATH}/qnx/scripts/sbl/ifs_qnx_dtb.lds. An excerpt of the linker script is shown below for reference:

/*
 * ifs_qnx.lds - simple linker file for stand-alone QNX IFS booting
 *
 * Copyright (C) 2020 Texas Instruments Incorporated - https://www.ti.com/
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE.txt file.
 */
OUTPUT_FORMAT("elf64-littleaarch64")
OUTPUT_ARCH(aarch64)
TARGET(binary)
INPUT(qnx-ifs)
INPUT(dtb.bin)
SECTIONS
{
 . = 0x0000000080080000;
 qnx = .;
 .qnx : { qnx-ifs }
 . = 0x0000000088000000;
 dtb = .;
 .dtb : { dtb.bin }
}

In this case the address 0x0000000088000000 should be updated to the newly desired DTB load address.

11.6.3. DTB Address Passing: SBL vs U-boot

There is a important difference in the mechanism in which U-boot vs. SBL pass the address of the DTB to the QNX image.

  • With the QNX provided U-boot instructions, the DTB address is passed by argument to the QNX image (via the register x1). For passing the DTB address by argument, the -u arg argument must be provided to the QNX IFS startup command. For example, from the J784S4 build file: [+keeplinked] startup-j784s4-evm -u arg -v -s1:1:1:2 -r0xA0000000,0x60000000,1....

  • In SBL, the DTB load address is passed to QNX from Arm Trusted Firmware (ATF) by value in the register x0. For passing the DTB address by argument, the -u reg argument must be provided to the QNX IFS startup command. For example, [+keeplinked] startup-j784s4-evm -u reg -v -s1:1:1:2 -r0xA0000000,0x60000000,1,1....

    • If using a custom ATF image for SBL that has been built outside of the PSDK QNX make system, make sure that the build flag K3_HW_CONFIG_BASE=$(FDT_LOAD_ADDR) is used.

Important

The default QNX IFS (j721e-evm-ti.build) uses the argument method for getting the DTB address. This means that the default QNX IFS is made for U-boot only (at least on SDP 800). The PSDK QNX make system will copy this build file and change -u arg to -u reg automatically for SBL (and name it j721e-evm-ti-sbl.build). If using a custom build file, make sure that the -u argument is set accordingly.