On Thu, May 17, 2018 at 07:48:45PM +0300, Ramon Fried wrote: > On Thu, May 17, 2018 at 5:22 PM, Tom Rini <tr...@konsulko.com> wrote: > > On Thu, May 17, 2018 at 02:01:55PM +0300, Ramon Fried wrote: > > > >> Hi. > >> I'm currently working on snapdragon bootloader support and in the > >> particular case where U-boot is running in Aarch32 and the kernel is > >> Aarch64 the specific implementation is to jump to Linux through SCM > >> call. > >> > >> I try to find the best possible way to provide an alternative boot > >> function. > >> Adding #ifdef ARCH_SNAPDRAGON will just be too specific in > >> arm/lib/bootm.c in my opinion and I'm thinking of introducing kind of > >> a callback function in gd. that if exists will jump there instead of > >> executing boot_jump_linux(). > >> > >> What do you think ? > > > > So, to be clear, we're on an aarch64 SoC, but U-Boot has been entered in > > 32bit mode. And we need to boot a 64bit Linux Kernel. What else, if > > anything, is also loaded/still in residence/etc? Can you explain the > > overall usecase a bit more and why we're in 32bit mode? Thanks! > > > OK. > Basically, Qualcomm has the following boot flow: > > PBL -> SBL -> LK -> Linux Kernel > > PBL - 32bit Primary boot loader(ROM) loads the SBL from eMMC. > > SBL - 32bit Secondary boot loader(eMMC/UFS), proprietary closed source, > Initializes the DDR, starts the trustzone and can load either a 32bit > or a 64bit (1) > ELF bootloader, given that it's signed. > > LK - Little kernel, 32bit. Qualcomm maintains a downstream version, open > source. > Loads 64bit Android boot image from eMMC and jumps to it using SMC > call made to Trustzone. > > This was used primarily for Android, but when Dragonboards boards came > out, Qualcomm and Linaro started > distributing 64bit Linux OE & Debian builds that were booted by LK. > Because U-boot is much more useful than LK, the first U-boot > contribution was made by Mateusz Kulikowski. > > Basically, Mateusz port is wrapping U-boot to appear as a kernel so LK > boots it, then it boots Linux. > So basically, LK did the 32 -> 64 transition. > > Now, here where I appear in the story... :)
Thanks for the detailed background. > I'm trying to get rid of LK and use U-boot as the real bootloader for Linux. > I succeeded in that, and I have all the patches ready for submission, > I just need to add a dedicated boot function > that does the SMC call, hence this discussion. > > (1) - It implies that we can in practice just use 64bit U-boot for Snapdragon. > The only problem I have right now is that there's isn't any > open-source tool to sign the Bootloader that supports ELF64 > executable. Is it possible to just write that tool, or update an existing tool to do that signature? -- Tom
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