[U-Boot] [RFC PATCH] dm: Add support for all targets which requires MANUAL_RELOC

[Albert ARIBAUD]

Hello Michal,

On Wed, 4 Feb 2015 10:56:02 +0100, Michal Simek
<michal.simek at xilinx.com> wrote:
> On 02/04/2015 04:11 AM, Masahiro Yamada wrote:
> > Hi Michal,
> > 
> > 
> > On Tue, 3 Feb 2015 10:11:39 +0100
> > Michal Simek <michal.simek at xilinx.com> wrote:
> > 
> >> Hi Simon,
> >>
> >> On 02/03/2015 03:02 AM, Masahiro Yamada wrote:
> >>> Hi.
> >>>
> >>>
> >>> On Mon, 2 Feb 2015 16:57:15 -0700
> >>> Simon Glass <sjg at chromium.org> wrote:
> >>>
> >>>> Hi Michal,
> >>>>
> >>>> On 2 February 2015 at 08:31, Michal Simek <michal.simek at xilinx.com> wrote:
> >>>>> Targets with CONFIG_NEEDS_MANUAL_RELOC do not use REL/RELA
> >>>>> relocation (mostly only GOT) where functions aray are not
> >>>>> updated. This patch is fixing function pointers for DM core
> >>>>> and serial-uclass to ensure that relocated functions are called.
> >>>>>
> >>>>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
> >>>>> ---
> >>>>>
> >>>>>  drivers/core/root.c            | 64 ++++++++++++++++++++++++++++++++++++++++++
> >>>>>  drivers/serial/serial-uclass.c | 16 +++++++++++
> >>>>>  2 files changed, 80 insertions(+)
> >>>>
> >>>> How long will we have to carry this patch? It seems that if we add any
> >>>> new driver we will have to add more code like this?
> >>>
> >>>
> >>>
> >>> This patch is unfortunate.
> >>> Can we discontinue CONFIG_NEEDS_MANUAL_RELOC some day?
> >>
> >> This patch (or similar one) has to be alive when we have platform
> >> which requires CONFIG_NEEDS_MANUAL_RELOC for full u-boot.
> >> There is an option to move to REL/RELA but the question is if
> >> all platforms have it/support it. Unfortunately I think that
> >> it will be in the tree for a long time.
> >>
> >>>
> >>> If we use SPL, we do not have to relocate code, I think.
> >>
> >> SPL doesn't have relocation that's why this code is not used there.
> >>
> > 
> > It is not what I meant.
> > 
> > 
> > If SPL can directly load the main u-boot image
> > to the DRAM address where it is linked,
> > we do not relocate the code in the main image.
> 
> Current behavior is that SPL is reading u-boot.img entry point which
> can be in any location and jump to it and u-boot self relocate to the end of
> memory.
> If SPL adds u-boot directly to the location where it should run after relocation
> then relocation is not needed.
> To ensure this capability (based on my poor GOT/REL/RELA) experience it means
> that SPL loads u-boot to that location and patch REL/RELA section based on this location
> and internal relocation should be skipped.

IOW, that SPL perform the work of relocate_code() in U-Boot -- at least,
on ARM, where REL/RELA is used.

> This is definitely doable for REL/RELA case and it can also speedup boot process

Not sure about the speed-up, but never mind.

> (I don't think there is easy way how to solve this with just GOT relocation because
> of that MANUAL_RELOC code which is patching arrays with function pointers).

Even without importing SPL in the equation, switching from GOT to
REL/RELA has enourmous advantages.

> Thanks,
> Michal

Amicalement,
-- 
Albert.