[U-Boot] initcall revisited - A new idea to discuss

[Graeme Russ]

Hi Wolfgang,

On Wed, Jan 4, 2012 at 1:44 AM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Graeme,
>
> In message <4F02DA64.60502 at gmail.com> you wrote:
>>

[snip]

>> INIT_FUNC(cpu_init_f, f, "fred", "blah", "foo");
>>
>> Generates the string:
>> f:cpu_init_f:"fred":"blah":"foo"
>>
>> and we can parse each of the elf archives to obtain a list of string
>> pointers from the .initfuncs, extract the strings and process them to
>> generate the init arrays
>>
>> and add:
>>
>>       /DISCARD/ : { *(.initfuncs*) }
>>
>> to the linker script to throw away the strings
>>
>> It's a tad ugly under the hood, but the output will be very clean
>>
>> Does this sound like a plan?
>
> Yes.  Looks good to me.
>
> One thing comes to mind: it would be nice if we can find a way that
> the INIT_FUNC definitions behave similar to "weak" functions - if an
> init_func can be redefined / overwritten / modified by board specific
> code we eventually have a very nice way to get rid of the related
> #ifdef's.

I have a thought on this. How about a SKIP_INIT macro. Here's the idea
using SDRAM as an example:

At the arch level you may have

INIT_FUNC(sdram_init, f, "sdram", "console","")

so sdram_init sets the "sdram" requisite and must be done after all
"console" requisites have been completed.

Now if a SoC or board has an init that must be done before SDRAM:

INIT_FUNC(pre_sdram_init, f, "pre_sdram", "", "sdram")

So this sets the pre_sdram requisite, requires no other initialisation
before running and must happen before and "sdram" init functions are run

Now lets say the Soc or board has a unique sdram init function that
overrides the arch's sdram init. We could just use weak functions and
allow the SoC or board to override sdram_init. But what if the SoC or
board has additional pre-requisite (or post-requisite) init requirements?

So in the SoC or board file:

SKIP_INIT(sdram)
INIT_FUNC(board_sdram_init, f, "board_sdram","pre_sdram,vreg,console", "")

Using "board_sdram" versus "sdram_init" is cricital:

The init sequence build tool will first create the entire init sequence
including the functions marked as "sdram" and "board_sdram". But after
building the arrays, it will strip out all the functions marked as "sdram"
init functions. The reason the entire list has to be build first is so the
functions that rely on "sdram" can be added without unmet prerequisite
errors.

Of course, if you use SKIP_INIT(foo), you need to make sure that any
replacement INIT_FUNC will do everything foo did to make your board work.

Interestingly, this allows the following:

INIT_FUNC(calc_relocation, fr, "calc_reloc", "sdram", "")
INIT_FUNC(copy_uboot_to_ram, fr, "copy_to_ram", "calc_relocation", "")
INIT_FUNC(do_elf_reloc_adjusments, fr, "elf_reloc", "copy_to_ram", "")
INIT_FUNC(clear_bss, fr, "clear_bss", "calc_reloc", "")

#ifdef CONFIG_SYS_SKIP_RELOCATION
SKIP_INIT(calc_reloc)
SKIP_INIT(copy_to_ram)
SKIP_INIT(elf_reloc)
#endif

So if CONFIG_SYS_SKIP_RELOCATION is defined, relocation is not performed,
but clear_bss still is

Regards,

Graeme