1*54fd6939SJiyong ParkRaspberry Pi 4 2*54fd6939SJiyong Park============== 3*54fd6939SJiyong Park 4*54fd6939SJiyong ParkThe `Raspberry Pi 4`_ is an inexpensive single-board computer that contains four 5*54fd6939SJiyong ParkArm Cortex-A72 cores. Also in contrast to previous Raspberry Pi versions this 6*54fd6939SJiyong Parkmodel has a GICv2 interrupt controller. 7*54fd6939SJiyong Park 8*54fd6939SJiyong ParkThis port is a minimal port to support loading non-secure EL2 payloads such 9*54fd6939SJiyong Parkas a 64-bit Linux kernel. Other payloads such as U-Boot or EDK-II should work 10*54fd6939SJiyong Parkas well, but have not been tested at this point. 11*54fd6939SJiyong Park 12*54fd6939SJiyong Park**IMPORTANT NOTE**: This port isn't secure. All of the memory used is DRAM, 13*54fd6939SJiyong Parkwhich is available from both the Non-secure and Secure worlds. The SoC does 14*54fd6939SJiyong Parknot seem to feature a secure memory controller of any kind, so portions of 15*54fd6939SJiyong ParkDRAM can't be protected properly from the Non-secure world. 16*54fd6939SJiyong Park 17*54fd6939SJiyong ParkBuild Instructions 18*54fd6939SJiyong Park------------------ 19*54fd6939SJiyong Park 20*54fd6939SJiyong ParkThere are no real configuration options at this point, so there is only 21*54fd6939SJiyong Parkone universal binary (bl31.bin), which can be built with: 22*54fd6939SJiyong Park 23*54fd6939SJiyong Park.. code:: shell 24*54fd6939SJiyong Park 25*54fd6939SJiyong Park CROSS_COMPILE=aarch64-linux-gnu- make PLAT=rpi4 DEBUG=1 26*54fd6939SJiyong Park 27*54fd6939SJiyong ParkCopy the generated build/rpi4/debug/bl31.bin to the SD card, adding an entry 28*54fd6939SJiyong Parkstarting with ``armstub=``, then followed by the respective file name to 29*54fd6939SJiyong Park``config.txt``. You should have AArch64 code in the file loaded as the 30*54fd6939SJiyong Park"kernel", as BL31 will drop into AArch64/EL2 to the respective load address. 31*54fd6939SJiyong Parkarm64 Linux kernels are known to work this way. 32*54fd6939SJiyong Park 33*54fd6939SJiyong ParkOther options that should be set in ``config.txt`` to properly boot 64-bit 34*54fd6939SJiyong Parkkernels are: 35*54fd6939SJiyong Park 36*54fd6939SJiyong Park:: 37*54fd6939SJiyong Park 38*54fd6939SJiyong Park enable_uart=1 39*54fd6939SJiyong Park arm_64bit=1 40*54fd6939SJiyong Park enable_gic=1 41*54fd6939SJiyong Park 42*54fd6939SJiyong ParkThe BL31 code will patch the provided device tree blob in memory to advertise 43*54fd6939SJiyong ParkPSCI support, also will add a reserved-memory node to the DT to tell the 44*54fd6939SJiyong Parknon-secure payload to not touch the resident TF-A code. 45*54fd6939SJiyong Park 46*54fd6939SJiyong ParkIf you connect a serial cable between the Mini UART and your computer, and 47*54fd6939SJiyong Parkconnect to it (for example, with ``screen /dev/ttyUSB0 115200``) you should 48*54fd6939SJiyong Parksee some text from BL31, followed by the output of the EL2 payload. 49*54fd6939SJiyong ParkThe command line provided is read from the ``cmdline.txt`` file on the SD card. 50*54fd6939SJiyong Park 51*54fd6939SJiyong ParkTF-A port design 52*54fd6939SJiyong Park---------------- 53*54fd6939SJiyong Park 54*54fd6939SJiyong ParkIn contrast to the existing Raspberry Pi 3 port this one here is a BL31-only 55*54fd6939SJiyong Parkport, also it deviates quite a lot from the RPi3 port in many other ways. 56*54fd6939SJiyong ParkThere is not so much difference between the two models, so eventually those 57*54fd6939SJiyong Parktwo could be (more) unified in the future. 58*54fd6939SJiyong Park 59*54fd6939SJiyong ParkAs with the previous models, the GPU and its firmware are the first entity to 60*54fd6939SJiyong Parkrun after the SoC gets its power. The on-chip Boot ROM loads the next stage 61*54fd6939SJiyong Park(bootcode.bin) from flash (EEPROM), which is again GPU code. 62*54fd6939SJiyong ParkThis part knows how to access the MMC controller and how to parse a FAT 63*54fd6939SJiyong Parkfilesystem, so it will load further components and configuration files 64*54fd6939SJiyong Parkfrom the first FAT partition on the SD card. 65*54fd6939SJiyong Park 66*54fd6939SJiyong ParkTo accommodate this existing way of configuring and setting up the board, 67*54fd6939SJiyong Parkwe use as much of this workflow as possible. 68*54fd6939SJiyong ParkIf bootcode.bin finds a file called ``armstub8.bin`` on the SD card or it gets 69*54fd6939SJiyong Parkpointed to such code by finding a ``armstub=`` key in ``config.txt``, it will 70*54fd6939SJiyong Parkload this file to the beginning of DRAM (address 0) and execute it in 71*54fd6939SJiyong ParkAArch64 EL3. 72*54fd6939SJiyong ParkBut before doing that, it will also load a "kernel" and the device tree into 73*54fd6939SJiyong Parkmemory. The load addresses have a default, but can also be changed by 74*54fd6939SJiyong Parksetting them in ``config.txt``. If the GPU firmware finds a magic value in the 75*54fd6939SJiyong Parkarmstub image file, it will put those two load addresses in memory locations 76*54fd6939SJiyong Parknear the beginning of memory, where TF-A code picks them up. 77*54fd6939SJiyong Park 78*54fd6939SJiyong ParkTo keep things simple, we will just use the kernel load address as the BL33 79*54fd6939SJiyong Parkentry point, also put the DTB address in the x0 register, as requested by 80*54fd6939SJiyong Parkthe arm64 Linux kernel boot protocol. This does not necessarily mean that 81*54fd6939SJiyong Parkthe EL2 payload needs to be a Linux kernel, a bootloader or any other kernel 82*54fd6939SJiyong Parkwould work as well, as long as it can cope with having the DT address in 83*54fd6939SJiyong Parkregister x0. If the payload has other means of finding the device tree, it 84*54fd6939SJiyong Parkcould ignore this address as well. 85