[U-Boot] [RFC] board_f: generalize code for case of no relocation

[Bin Meng]

Hi Alexey,

On Thu, Dec 17, 2015 at 3:13 AM, Alexey Brodkin
<Alexey.Brodkin at synopsys.com> wrote:
> Hi Bin,
>
> On Tue, 2015-12-15 at 20:45 +0800, Bin Meng wrote:
>> On Tue, Dec 15, 2015 at 6:06 PM, Alexey Brodkin
>> <Alexey.Brodkin at synopsys.com> wrote:
>> > Current implementation of disabled relocation only works for EFI.
>> >
>> > In case of GD_FLG_SKIP_RELOC jump_to_copy() will return instead of
>> > jumping further in board_init_r() etc. And jump_to_copy() being the last
>> > call in init_sequence_f when returning simply triggers hang() in
>> > board_init_f(). Well for everything except ARM, SANDBOX and EFI_APP.
>> >
>> > Not sure why ARM and SANBOX are here - I would assume it's all on
>> > purpose but as for EFI_APP this is an essential need for getting out of
>> > board_init_f() and jumping in board_init_r() immediately afterwards, see
>> > efi_main().
>> >
>> > But what if in case of no relocation we jump in board_init_r() right
>> > from jump_to_copy()? In that case we remove one ifdef from
>> > board_init_f() and leave a chance to seamlessly re-use disabled
>> > relocation for other (non-EFI) cases.
>> >
>> > Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
>> > ---
>> >
>> > Note I didn't test it for EFI because I don't know how to do that in
>> > simulation, please let me know if there's a simple way to do it.
>> >
>>
>> Does doc/README.efi not help?
>
> Yeah thanks for that obvious pointer.
> Still it requires some extra steps like obtaining/building EFI BIOS etc.
> Anyways I'll try to get this setup up and running.
>
>>
>> > But I did test it for ARC boards (with additional patches) that enable
>> > disabled relocation - these patches to follow once something similar to
>> > my proposal here is implemented.
>> >
>>
>> Reviewed-by: Bin Meng <bmeng.cn at gmail.com>
>>
>> Tested on QEMU, booting u-boot-app.efi with EFI firmware
>> Tested-by: Bin Meng <bmeng.cn at gmail.com>
>>
>> >  common/board_f.c  | 11 ++++++++---
>> >  lib/efi/efi_app.c |  2 +-
>> >  2 files changed, 9 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/common/board_f.c b/common/board_f.c
>> > index eac7c5e..2d60ed9 100644
>> > --- a/common/board_f.c
>> > +++ b/common/board_f.c
>> > @@ -720,8 +720,14 @@ static int setup_reloc(void)
>> >
>> >  static int jump_to_copy(void)
>> >  {
>> > +       /*
>> > +        * In case of no relocation nothing to do between "running from flash"
>> > +        * (init_f) and "running from ram" (init_r), so just jumping in
>> > +        * board_init_r().
>> > +        */
>> >         if (gd->flags & GD_FLG_SKIP_RELOC)
>> > -               return 0;
>> > +               board_init_r((gd_t *)gd, gd->relocaddr);
>
> I tried to do more complicated things compared to booting in console
> like "usb start" and at that point faced an unexpected problem.
>
> The thing is usually in between board_init_f() and board_init_r()
> we do a couple of things, most important for us here is stack pointer
> update. See in board_init_f() we use init stack which is usually
> (for most of arches except x86) is located at hardcoded address
> CONFIG_SYS_INIT_SP_ADDR which might easily point to quite limited special
> memory like on-chip SRAM or (which is the case) be in the very beginning of
> RAM.
>
> This init stack as said above could be quite small - just enough for every
> everything in board_init_f(). But when something heavy is executed what may
> easily happen (and that happens for me on "usb start") - we'll get in unexpected
> memory location. In my case I'm hitting non-existing memory which precedes
> DDR. And that was quite fortunate because I was hitting exception and so
> was able to figure out what's wrong.
>
> For me solution was in stack-pointer update right before calling board_init_r()
> in my start.S. And that required another line addition to jump_to_copy():
> So now I'm having this:
> ------------------>8-----------------
>         if (gd->flags & GD_FLG_SKIP_RELOC) {
>                 board_init_f_stack_update(gd->start_addr_sp); <-- Updating SP
>                 board_init_r((gd_t *)gd, gd->relocaddr);
>         }
> ------------------>8-----------------
>
> I'm not sure if all that makes sense for x86 EFI but would like to know
> your opinion if potential run out out stack may happen there as well.
>

For u-boot-app.efi, the stack is allocated by the EFI firmware, so I
think we are fine here. If we change its SP without making the EFI
firmware aware, I believe subsequent call to EFI boot services will
fail.

Regards,
Bin