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

[Heiko Schocher]

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 ...

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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