[Arm-dev] Why RPi3 under Arm32 rather than AArch64?

[Gordan Bobic]

On Mon, Jan 8, 2018 at 11:35 AM, Johnny Hughes <johnny at centos.org> wrote:

> On 01/04/2018 04:30 PM, Gordan Bobic wrote:
> > Things required to "support" Pi3 aarch64 that aren't already in place in
> > core CentOS (or at least I haven't managed to find them):
> >
> > 1) Pi3 firmware blobs
> > Trivially downloadable from
> > https://github.com/raspberrypi/firmware/tree/master/boot
>
> I assume we include those in our armhfp kernel so this is not a problem
> for an official CentOS image.
>
> >
> > 2) UEFI bootloader
> > There are two options, u-boot and Tianocore.
> > My current Pi3 aarch64 image works with u-boot that I grabbed from the
> > Fedora 26 image.
> > I'm currently trying to get it working with Tianocore from here:
> > https://github.com/andreiw/RaspberryPiPkg
> > I _almost_ have it working (gets as far as booting grub, but grub then
> > doesn't manage to boot up the kernel, almost certainly a dtb issue
> > somewhere).
>
> We kind of need to be able to BUILD this, not just take it from
> something else an use it.  At least that is certainly preferable. I
> suppose we can just include it as a SOURCE for the SRPM, but that is not
> ideal.
>

Yes, I built it from source, so that part won't be a problem.



>
> >
> > 3) Kernel
> > I keep my own mainline kernel build for aarch64, loosely based on, IIRC,
> > 4.5.x that shipped with CentOS aarch64, but with some modifications. I
> > have a build that works on both my X-Gene and the Pi3. You can find it
> here:
> > http://ftp.redsleeve.org/pub/misc/kernel/aarch64/RPMS/
> > (Note: I only included Pi 3 SoC configuration as of 4.9.73).
> >
> > So it's not exactly an insurmountable problem, it's just a case off
> > dropping a tarball of 5-6 files onto the /boot/efi FAT partition, having
> > the appropriate kernel installed in the image, and it should "just work".
> > I can have a working image with u-boot EFI as soon as I find half an
> > hour to spare.
> > The one with Tianocore EFI will take a little longer.
> >
>
> Is there something about OUR generic CentOS 4.9.x kernel SRPM that does
> not work if compiled on aarch64:
>
> http://vault.centos.org/altarch/7.4.1708/experimental/Source
> /i386/Source/SPackages/
>
> That SRPM is what we use for i386/x86_64 and the generic armhfp kernel.
> If we need a new config file, we can likely figure that out.
>
> We would obviously need to add in whatever is necessary for the firmware
> blobs and the pi uboot config, etc.
>


You will need to build it for aarch64 and add the support for the relevant
SoCs and the hardware required to boot on them.
Other than that, no, there is no reason unless some of the added patches
break something outside of the config being used (something that is not
0-risk in my experience).

Other than that the reason I build my own is because when it comes to
kernels I am much more comfortable sticking to the LT mainline than a
distro modified kernel.
I am happy to go into details of why this has been the case for a long
time, but that really is something for another thread, and possibly better
not a public one.



>
> I am not opposed to doing this if we can do it right .. which is that it
> is secure and reproducible to build and install via the RPMs (the
> kernel), which are produced completely produce automatically from the
> SRPM ..


My kernels are build from SRPMs containing a plain upstream LT kernel with
no extra patches.
So the method is sound. The only thing I can think of that could
potentially break it is if a patch in the CentOS kernel breaks something
for SoCs that aren't included in the existing kernel config.



> AND for the image, it is completely buildable via a kickstart
> file or one of the normal tools and everything does not have to be hand
> added, etc.  If we can make that happen, then I am happy for us to have
> an aarch64 build.
>

Yes, all of that is doable.



>
> But, it is odd that the RPI foundation doesn't care enough to make that
> happen.
>

OK, I just lost you there - what part of the above would you consider to be
in their remit to do?



>
> We might get some ideas from the SRPMS these guys do:
>
> https://www.linux.com/news/learn/intro-to-linux/first-64-bit
> -and-enterprise-os-comes-raspberry-pi-3
>


I don't really see where the difficulty in any of this is. My intention has
always been for the
final image to contain nothing in it that wasn't installed from an RPM -
and as soon as I
have Tianocore working properly, I will produce it. If there is interest in
the u-boot UEFI
based image, I believe that can already be done (depending on whether any
minor changes
are required to the u-boot SRPMs from F26).

Gordan
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