[U-Boot] [PATCH v2 23/23] sunxi: A64: add 32-bit SPL support

[André Przywara]

On 05/12/16 06:26, Simon Glass wrote:
> Hi Andre,
> 
> On 4 December 2016 at 18:52, Andre Przywara <andre.przywara at arm.com> wrote:
>> When compiling the SPL for the Allwinner A64 in AArch64 mode, we can't
>> use the more compact Thumb2 encoding, which only exists for AArch32
>> code. This makes the SPL rather big, up to a point where any code
>> additions or even a different compiler may easily exceed the 32KB limit
>> that the Allwinner BROM imposes.
>> Introduce a separate, mostly generic sun50i-a64 configuration, which
>> defines the CPU_V7 symbol and thus will create a 32-bit binary using
>> the memory-saving Thumb2 encoding.
>> This should only be used for the SPL, the U-Boot proper should still be
>> using the existing 64-bit configuration. The SPL code can switch to
>> AArch64 if needed, so a 32-bit SPL can be combined with a 64-bit U-Boot
>> proper to eventually launch arm64 kernels.
> 
> So if I understand correctly, you want SPL to be 32-bit and U-Boot
> proper to be 64-bit?

Yes, that is _one_ possible option, mostly driven by size constraints
and due to AArch64 code being much bigger than Thumb2.

> And you are adding a new board config for that?

Yes, for now this one (separate) defconfig aims to cover all A64 boards.
This is not ideal (as Maxime pointed out already), so if you know a nice
way of using a single defconfig for one board and configuring it once
with CPU_V7 and then again with ARM64 set, I am all ears.

Also I haven't found a make target to just build the SPL (possibly
another one for just the U-Boot proper). Maybe this would help things?

> Instead, can you do something similar to tegra, which uses ARMv4t for
> SPL and ARMv7 for U-Boot proper?

You will need two different (cross-)compilers, so just setting some
compiler options will not help.
Besides compiling the SPL as 32-bit is only an option, the SPL also
works as a pure 64-bit binary. And people expressed the wish of having
the option of using both ways - at least for the time being.

Cheers,
Andre.

>>
>> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
>> ---
>>  board/sunxi/Kconfig            | 14 ++++++++++++--
>>  configs/pine64_plus_defconfig  |  2 +-
>>  configs/sun50i_spl32_defconfig | 10 ++++++++++
>>  include/configs/sunxi-common.h |  2 +-
>>  4 files changed, 24 insertions(+), 4 deletions(-)
>>  create mode 100644 configs/sun50i_spl32_defconfig
> 
> Regards,
> Simon
>