[U-Boot] powerpc SPL framework: Avoiding relocate_code

[Prabhakar Kushwaha <prabhakar@freescale.com>]

On 09/12/2013 11:28 PM, Scott Wood wrote:
> On Mon, 2013-09-09 at 16:43 +0530, Prabhakar Kushwaha wrote:
>> Hi,
>>
>>    SPL framework is used to support multi-stage booting.  Where first
>> level boot loader is created via SPL having relocate_code() function.
>> I am working on a Freescale's SoC which has less internal SRAM.
>> I don't want to use relocate_code() as to support this function, I need
>> to reduce SPL bin  to SRAM/2 size.
>>
>> is there way to avoid relocate_code function ?
>>
>> I tried with below sequence, but it is not working for me :(
>>
>>       .globl    relocate_code
>> relocate_code:
>>       mr    r1,r3        /* Set new stack pointer        */
>>       mr    r9,r4        /* Save copy of Init Data pointer    */
>>       mr    r10,r5        /* Save copy of Destination Address    */
>>
>>       GET_GOT
>> #ifndef CONFIG_SPL_BUILD
>>
>> --
>> --
>> #endif
>>       .globl    in_ram
>> in_ram:
> Well, you certainly don't want to disable it for all SPLs...

it should be disabled for those SPL which relocate itself in SRAM, for 
other no

>> The reason is bss "variables" which are mapped to 0x0000_0000 onwards
>> because "bss"section are mapped after 0xfffffffc in lds. They are not
>> available during SPL execution.  is there way to relocate bss section in
>> the execution range of SPL?
> Are you talking about a scenario in which the SPL is loaded into SRAM
> rather than (e.g.) the NAND buffer?  In that case, why is U-Boot not
> linked at the actual SRAM address?  No copy should be needed in that
> case, and the BSS will not be at zero.

I am linking SPL with the address of SRAM as I want resetvec at 
0xfffffffc but  still I am finding bss at 0x0

in  u-boot-spl.lds we have :-

#ifdef CONFIG_SYS_MPC85XX_NO_RESETVEC
     .bootpg ADDR(.text) - 0x1000 :
     {
         KEEP(*(.bootpg))
     } :text = 0xffff
#else
     .resetvec ADDR(.text) + RESET_VECTOR_OFFSET : {
         KEEP(*(.resetvec))
     } = 0xffff
#endif

     /*
      * Make sure that the bss segment isn't linked at 0x0, otherwise its
      * address won't be updated during relocation fixups.
      */
     . |= 0x10;

     . = ALIGN(4);
     __bss_start = .;
     .bss : {
         *(.sbss*)
         *(.bss*)
     }
     . = ALIGN(4);
     __bss_end = .;

from above lds, we put resetvec at 0xfffffffc And place BSS just after 
it. Hence at 0x0.
Ideally __bss_start should not be put after 0xfffffffc as it is making 
relocation a requirement.

Regards,
Prabhakar