[U-Boot] [PATCH v4 26/26] sunxi: A64: add 32-bit SPL support

[Andre Przywara]

Hi,

On 13/01/17 02:19, Simon Glass wrote:
> Hi Andre,
> 
> On 2 January 2017 at 04:48, 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.
>>
>> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
>> ---
>>  board/sunxi/Kconfig            | 14 ++++++++++++--
>>  configs/pine64_plus_defconfig  |  2 +-
>>  configs/sun50i_spl32_defconfig | 10 ++++++++++
>>  3 files changed, 23 insertions(+), 3 deletions(-)
>>  create mode 100644 configs/sun50i_spl32_defconfig
> 
> Following up on the previous discussion, I take it that one on problem
> is that U-Boot does not support building SPL with one toolchain and
> U-Boot proper with another?

Yes. For the time being I have a script [1] that first configures and
compiles everything with an ARM cross compiler, then repeats this with
an aarch64 cross compiler. Then I combine the 32-bit SPL and the 64-bit
U-Boot proper.

While we are at it: I didn't find a Makefile target to just compile the
SPL (or just U-Boot proper), is that worth looking at? Or can we somehow
influence Kconfig options on the command line to achieve that on that level?

> Re wanting to build SPL either as 32-bit or 64-bit, could this be a
> Kconfig option perhaps?

Sounds like a direction worth to investigate.
In the moment we have two separate defconfig files, because CPU_V7 and
ARM64 are actually mutually exclusive, which is really a pain and the
main reason that part wasn't merged.

> Anyway, if this is what we have for now, fine. But I'd like to see at
> least a TODO suggesting a better solution.

So yes, the series was now merged omitting the 32-bit SPL part, which is
really optional. For the time being we seem to get away with only
64-bit, but I will definitely revisit this after having handled the
higher priority patches in my queue.

Cheers,
Andre.

[1] http://pastebin.com/kH7u2h7M