On Fri, May 25, 2018 at 05:41:31PM +0300, Ramon Fried wrote: > On Fri, May 25, 2018 at 3:11 PM, Tom Rini <tr...@konsulko.com> wrote: > > 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? > Yes. It should be possible. > > Actually, when I did have access to qcom internal tool for doing so I > was able to run U-boot > on 64bit mode. I had problems booting the kernel, as after the boot > weird things were happening, > like other cpu weren't responding, eMMC driver wasn't working etc. > I suspect it's related to low level initialization that was lacking, > or something similar. > > I ended up working on the 32bit mode because I no longer have access > to the internal tool. > I believe that in the end we will end up with a working 64bit version. > I'm just thinking that meanwhile It maybe worthwhile to also have the > 32bit version. > > What do you think ?
How long might we be in this interim odd spot? It sounds like we need some odd hoops to go and be able to boot a 64bit Linux when we're in 32bit mode. If this is just for a short period of time, maybe we just accept that the Linaro tree will have to hold a patch or two for now until we can just be a good and clean 64bit binary? -- Tom
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