[U-Boot] [RFC PATCH 0/2] ARMv8 Aarch32 support

[Peter Robinson]

>> >> I've been working with Soby Mathew to get U-Boot booting on ARM's
>> >> AEMv8 FVP model in Aarch32 mode.
>> >>
>> >> Soby worked out what needed to be changed and I'm refining the changes
>> >> into patches that can be built for both Aarch64 and Aarch32 mode.
>> >>
>> >> There are two patches for discussion:
>> >>
>> >> [RFC PATCH 1/2] Add Aarch32 option for ARMv8 CPUs
>> >> [RFC PATCH 2/2] Add vexpress_aemv8a_aarch32 variant
>> >>
>> >> I expect the first patch to be controversial.  I also don't expect it to
>> >> be accepted, but to demonstrate what changes we needed to make to get an
>> >> ARMv8 platform to boot in Aarch32 mode when selecting CPU_V7 instead of
>> >> ARM64 as the CPU type.  This in itself may be the wrong approach.
>> >>
>> >> It adds an ARMV8_AARCH32 config option and some checks in generic code
>> >> for that option to allow the code to differentiate between the two
>> >> modes.
>> >>
>> >> The second patch should be less controversial.  It adds support for a
>> >> new AEMv8 variant that runs in 32-bit mode.  The most awkward part is
>> >> that it defines itself not as ARM64, but as CPU_V7.  I expect this to
>> >> change based on feedback from patch 1/2.
>> >>
>> >> The Aarch32 code runs on the same AEMv8 model as the Aarch64 code, but
>> >> takes an extra per-core model launch parameter to switch the cores into
>> >> Aarch32 mode, eg. "-C cluster0.cpu0.CONFIG64=0".
>> >
>> > So my first and slightly ignorant question is, why isn't this just a new
>> > regular ARMv7 board being added rather than a special cased ARMv8?
>> >
>>
>> That's a valid question.
>>
>> I guess it could be either.  At the moment, it's a bit of both.
>> arch/arm/Kconfig says it's an ARMv7, but then it's added to
>> board/armltd/vexpress64/Kconfig to re-use vexpress_aemv8a.h.
>>
>> But there's no reason it couldn't be added to
>> board/armlt/vexpress/Kconfig and have a copy of vexpress_aemv8a.h that
>> isn't special cased at all.  That approach seems more copy/paste-y
>> than what I've done in this series, though.
>>
>> I think the whole setup for vexpress/vexpress64 and AEMv8/Juno is
>> confused.  Really, all of these armlt boards are the same with minor
>> variations, even if the minor variation could be ARMv7 vs ARMv8.
>
> Maybe this gets to the heart of the problem then, and we should
> re-structure and fix this.  If you look in board/raspberrypi/rpi/ we
> support rpi1 2 and 3, and that includes rpi3 in 64bit mode.  So if we
> want to re-work board/armlt/vexpress/ to support the various ways the
> base hardware can be (/ has been over the years), lets.  Does that sound
> like a plan?

That sounds great to me, I would like to be able to use the vexpress
u-boot through qemu but be able to pass through the qemu generated DT
so as to get the HW passed through correctly. I'm interested as it
makes for a nice means of automation for some of my testing but also
for virt based build systems too.

Peter