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

[Dr. Philipp Tomsich]

> On 19 Sep 2017, at 11:12, Heiko Stübner <heiko at sntech.de> wrote:
> 
> Am Dienstag, 19. September 2017, 11:10:29 CEST schrieb 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.
> 
> From this conversation, it looks to me that I should wait for that new
> version for testing on rk3188, as it will likely show the same issues, right?

Yes.