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

[Dr. Philipp Tomsich]

Heiko,

> On 19 Sep 2017, at 12:16, Dr. Philipp Tomsich <philipp.tomsich at theobroma-systems.com> wrote:
> 
>> 
>> 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.

A new version with a reworked setjmp/longjmp implementation is available at
	https://patchwork.ozlabs.org/project/uboot/list/?series=4327

This passed testing for Andy (see the Tested-by: credit) on the boards he works
on, but is still pending a test of a RK3188.

Regards,
Philipp.