[U-Boot] [PATCH v2 0/5] rockchip: back-to-bootrom: replace assembly-implementation with C-code

[Dr. Philipp Tomsich]

Andy,

> On 19 Sep 2017, at 09:19, Andy Yan <andy.yan at rock-chips.com> wrote:
> 
> Hi Philipp:
> 
> 
> On 2017年09月19日 10:06, Andy Yan wrote:
>> Hi Philipp:
>> 
>> 
>> On 2017年09月19日 02:18, Philipp Tomsich wrote:
>>> Recent discussions confirmed (what the code always assumed): the
>>> Rockchip BROM always enters U-Boot with the stack-pointer valid
>>> (i.e. the U-Boot startup code is running off the BROM stack).
>>> 
>>> We can thus replace the back-to-bootrom code (i.e. both the
>>> save_boot_params and back_to_bootrom implementations) using C-code
>>> based on setjmp/longjmp.  The new implementation is already structured
>>> to allow an easy drop-in of Andy's changes to enter download-mode when
>>> returning to the BROM.
>>> 
>>> This entails one minor tweak to asm/system.h, which only exported
>>> the save_boot_params_ret prototype for ARMv7, but not for AArch64.
>>> 
>>> For v2, we force bootrom.o to alway be emitted as A32 (not T32), so we
>>> can safely call save_boot_params_ret().
>> 
>>    This still have a problem, because the setjmp  implementation for ARM32 platform  has humb code when CONFIG_SYS_THUMB_BUILD is
>> enabled, this is a default setting for most ARMv7 boards.
>> #if CONFIG_IS_ENABLED(SYS_THUMB_BUILD)
>> ".align 2\n"
>> "adr r0, jmp_target\n"
>> "add r0, r0, $1\n"  // r0 stored the jump target address and with bit[0] = 1, this will trigger a thumb switch in longjmp with code "bx r0"
>> #endif
>> 
>> When I force the setjmp code go arm code path, I can back to bootrom successfully, But I got a data abort exception in later. it seems it happens when bootrom finished the uboot code
>> copy, when jump to sdram, I need a further debug.
> 
> I found that r9 also need to be preserved, it seems that it hold the sdram base.

Thanks for testing and debugging: this is invaluable support, as I only have AArch64 boards to test.

The r9 issue will be easy enough to resolve.
However, it looks like I will need more work on setjmp/longjmp to make this safe both for T32 and A32.
Plus: I need to figure out why this didn’t show in my disassembly (I don’t remember whether it was a rk3188 or rk3288 board I looked at).

Might be tomorrow or Thursday until I can provide an new version.

Regards,
Philipp.