Ramon, Tom,
On Sat, May 26, 2018 at 7:58 AM, Ramon Fried ramon.fried@gmail.com wrote:
On Sat, May 26, 2018 at 5:18 AM, Tom Rini trini@konsulko.com wrote:
On Fri, May 25, 2018 at 05:41:31PM +0300, Ramon Fried wrote:
On Fri, May 25, 2018 at 3:11 PM, Tom Rini trini@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 trini@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?
I added Nicolas from Linaro to the thread so he can comment regarding the signing tool.
thanks Ramon, for the very good and information data above!
I agree with you that the jump through SCM call is very specific. I didn't send any of the 32bit patches yet, I was waiting to see if the required supported changes will get accepted. It's up to you to decide if you're willing to accept that as in intermediate solution until we get a working 64bit version. I do know that there is high demand in the community for such support.
The 32bit potentially waiting to be upstreamed is in my github repo here: https://github.com/mellowcandle/u-boot/tree/upstream
I have looked at the QCOM signing scripts, and I think they are now fixed and should work for ELF32 and ELF64. So we should be good to go with uboot built for aarch64!
Thanks, Ramon.
-- Tom
U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot