[U-Boot] [PATCH 6/9] sunxi: allow 32-bit builds for 64-bit SoCs

[Alexander Graf]

On 26.02.19 00:32, Andre Przywara wrote:
> Hi Alex,
> 
> On 2/22/19 2:13 AM, Alexander Graf wrote:
>>
>>
>> On 21.02.19 02:30, Andre Przywara wrote:
>>> At the moment we build the SPL and U-Boot proper for the 64-bit AArch64
>>> instruction set. But since the cores provide an AArch32 compatibility
>>> mode
>>> and in fact the BootROM runs in 32-bit mode, it can be useful to have at
>>> least the SPL run in AArch32 as well. This has two advantages:
>>> - As AArch32 features the compact Thumb2 instruction encoding, we can
>>>    get a much smaller image size, which is a relief for our SPL.
>>> - Staying in AArch32, with the MMU turned off, allows an easy return to
>>>    the BootROM and its FEL mode. This enables FEL booting on those SoCs.
>>>
>>> Introduce a Kconfig option which toggles between CONFIG_ARM64 and
>>> CONFIG_CPU_V7A, to allow easy switching between the two modes. This can
>>> be manually selected in menuconfig, but follow-up patches will introduce
>>> a separate defconfig for that purpose.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
>>> ---
>>>   arch/arm/mach-sunxi/Kconfig | 13 ++++++++++---
>>>   1 file changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
>>> index 74e234cded..347d737fd0 100644
>>> --- a/arch/arm/mach-sunxi/Kconfig
>>> +++ b/arch/arm/mach-sunxi/Kconfig
>>> @@ -146,6 +146,10 @@ config SUNXI_DRAM_MAX_SIZE
>>>       default 0xC0000000 if MACH_SUN50I || MACH_SUN50I_H5 ||
>>> MACH_SUN50I_H6
>>>       default 0x80000000
>>>   +config SUNXI_ARMV8_32BIT_BUILD
>>> +    bool "Build 32-bit binaries for ARMv8 SoCs"
>>> +    default n
>>> +
>>>   choice
>>>       prompt "Sunxi SoC Variant"
>>>       optional
>>> @@ -275,7 +279,8 @@ config MACH_SUN9I
>>>     config MACH_SUN50I
>>>       bool "sun50i (Allwinner A64)"
>>> -    select ARM64
>>> +    select ARM64 if !SUNXI_ARMV8_32BIT_BUILD
>>
>> Can't you make this "imply ARM64" instead and then just set
>> ARM64=n;CPU_V7A=y in the defconfig?
> 
> Ha, that indeed sounds tempting, and actually I tried this before, but
> it doesn't work. The kernel doc says that an "imply" setting can be
> overwritten by a direct dependency or a visible prompt. ARM64 is not
> visible (empty bool), so I figured that introducing this simple symbol
> is the smallest pain to tackle this issue.

If you say you already did try imply, then I'm all happy :).


Alex