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

[Michal Simek]

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

Thanks,
Michal