[U-Boot] passing info from SPL to U-Boot

[Stefano Babic]

Hi Heiko,

On 13/03/19 08:44, Heiko Schocher wrote:
> Hello Wolfgang,
> 
> Am 12.03.2019 um 18:46 schrieb Wolfgang Denk:
>> Dear Tom,
>>
>> In message <20190312173125.GP4690 at bill-the-cat> you wrote:
>>>
>>>> I think you were misled by Heiko's description.  What he really ment
>>>> was just that the addresses where the boot ROM stored the
>>>> information about the boot device etc. gets overwriteen when the SPL
>>>
>>> For clarity, that's not _quite_ it.  The ROM passes the value in a
>>> register and we move that to scratch space, see
>>> arch/arm/mach-omap2/lowlevel_init.S and save_boot_params.  This is done
>>> on every 32bit Cortex-A TI platform.
>> ...
>>> OK, but here's the problem.  We define off, iirc, 1KiB of that SRAM
>>> space as not-stack but scratch space to store stuff in.  The first
>>> problem you will hit, if something else touches that scratch space is
>>> what Heiko found, the boot value got blown away.
>>
>> I see.  Well, I think it's best if Heiko explains in detail; what he
>> has observed, and what when which part of the information got lost.
>> I was just interpreting his mail, so I may easily have misunderstood
>> this.
>>
>> @ Heiko:  Can you please elucidate?
> 
> arch/arm/include/asm/arch-am33xx/omap.h
> 
>  19 #ifdef CONFIG_AM33XX
>  20 #define NON_SECURE_SRAM_START   0x402F0400
>  21 #define NON_SECURE_SRAM_END     0x40310000
>  22 #define NON_SECURE_SRAM_IMG_END 0x4030B800
>  23 #elif defined(CONFIG_TI816X) || defined(CONFIG_TI814X)
>  24 #define NON_SECURE_SRAM_START   0x40300000
>  25 #define NON_SECURE_SRAM_END     0x40320000
>  26 #define NON_SECURE_SRAM_IMG_END 0x4031B800
>  27 #elif defined(CONFIG_AM43XX)
>  28 #define NON_SECURE_SRAM_START   0x402F0400
>  29 #define NON_SECURE_SRAM_END     0x40340000
>  30 #define NON_SECURE_SRAM_IMG_END 0x40337DE0
>  31 #define QSPI_BASE              0x47900000
>  32 #endif
>  33 #define SRAM_SCRATCH_SPACE_ADDR (NON_SECURE_SRAM_IMG_END - SZ_1K)
>  34
> 
> 
> and with ./include/configs/ti_armv7_common.h
> 
>  69 #ifndef CONFIG_SYS_INIT_SP_ADDR
>  70 #define CONFIG_SYS_INIT_SP_ADDR         (NON_SECURE_SRAM_END - \
>  71                                                
> GENERATED_GBL_DATA_SIZE)
>  72 #endif
>  73
> 
> include/generated/generic-asm-offsets.h
> 
>   9 #define GENERATED_GBL_DATA_SIZE 224 /* (sizeof(struct global_data) +
> 15) & ~15  @ */
>  10 #define GENERATED_BD_INFO_SIZE 112 /* (sizeof(struct bd_info) + 15)
> & ~15       @ */
>  11 #define GD_SIZE 224 /* sizeof(struct global_data)       @ */
> 
> 
> -> CONFIG_SYS_INIT_SP_ADDR = 0x40340000 - 0xe0  = 0x4033ff20
> -> SRAM_SCRATCH_SPACE_ADDR = 0x40337DE0 - 0x400 = 0x403379e0
> 
> ./arch/arm/include/asm/omap_common.h:
> 816 #define OMAP_SRAM_SCRATCH_BOOT_PARAMS   (SRAM_SCRATCH_SPACE_ADDR +
> 0x24)
> 
> OMAP_SRAM_SCRATCH_BOOT_PARAMS = 0x40337a04
> 
> So stack is on a higher address than the scratch space. Stack
> addresses decrement on usage, so may they overwrite scratch
> space, as SPL functionality grows more and more ...

What about to move this area after the initial SP ? This is the same way
we do with GENERATED_GBL_DATA_SIZE to avoid to be overwritten.

Stefano

> 
> Hmm... I see, the NON_SECURE_SRAM_IMG_END is fix defined, and we cannot
> move it.
> 
> Ok, looking on my own now on the hardware:
> 
> => md 40337a04
> 40337a04: 40338dc4 8f943b1e 8138beca 4ea1b2c2    ..3 at .;....8....
>           ^
>           pointer to bootparms struct
> 
> => md.b 40338dc4
> 40338dc4: ff ff ff ff 08 8f 33 40 07 01 00 00 00 00 00 00   
> ......3 at ........
>                                   ^^
>                                   bootmode 0x07 -> mmc0
> 
> Nothing overwritten here! Puuh...
> 
> But I have a bad feeling reading the bootmode again from U-Boot, as
> the boot_params info is may in space, where stack can overwrite it ...
> 
>>> I agree here.  Fixing things up such that we can pass things we know
>>> =66rom one stage to another in a defined manner, rather than ad-hoc
>>> manner, is good.  We could even, probably, re-work most of that use of
>>> scratch space to be done in another way, or make it safe to re-use
>>> later.
>>
>> Thanks a lot!  Let's go for it.
> 
> To be safe here, we should really pass the bootmode (or more common,
> the infos collected already in GD) from SPL to U-Boot ...
> 
> bye,
> Heiko


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