[U-Boot] [PATCH] libfdt: Add option to disable arch_fixup_fdt() calls

[Alexander Graf]

On 10.06.16 13:07, Michal Simek wrote:
> On 9.6.2016 16:40, Alexander Graf wrote:
>> On 06/09/2016 04:32 PM, Michal Simek wrote:
>>> On 9.6.2016 16:29, Alexander Graf wrote:
>>>> On 06/09/2016 04:23 PM, Michal Simek wrote:
>>>>> Disable arch_fixup_fdt() calls for cases where U-Boot shouldn't update
>>>>> memory setup in DTB file.
>>>>> One example of usage of this option is to boot OS with different memory
>>>>> setup than U-Boot use.
>>>>>
>>>>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
>>>> Could we instead just have the board file provide a fixup? It could then
>>>> also fix up the efi memory map.
>>> Not sure what exactly you are asking for.
>>> Do you mean to add fixup function to board file and overwrite default
>>> one?
>>
>> You have to touch some other code anyway to make this work with a
>> particular board, right? In that case, you can as well add a function to
>> the board file that explicitly provides a different, known good memory map.
> 
> I cant' see the reason to touch particular board. In past AMP solution
> where one core use the part of memory and second another part was the
> reason I needed this.
> For ARM64 case as you know from arm IRC I was trying to boot Linux from
> memory above 32bit space and for these tests I need to convince u-boot
> not to touch dtb memory setup.
> 
> But for the same board I want to use standard behavior but for some case
> this needs to be enabled.

For that particular case, can you try to see whether you can convince
U-Boot to just run in high memory instead? That would make things much
more consistent IMHO.

Giving U-Boot and Linux different views of the memory map is really just
asking for trouble. You'd have to make sure that you flush your caches
for example so that Linux doesn't suddenly get memory overwritten from
stale cache entries on the low memory even though Linux is already
accessing the high addresses.

For testing, sure, but to actually make use of it I'd rather see a clean
solution.


Alex