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

["Heiko Stübner" <heiko@sntech.de>]

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@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?


Heiko