[U-Boot] [PATCH] arch: armv8: Remove the error when dcache is off

[Alexander Graf]

On 27.06.17 13:20, Michal Simek wrote:
> Hi,
> 
> On 27.6.2017 13:01, Alexander Graf wrote:
>> I don't think that's going to work - at least not without compiler flag
>> changes. By default, gcc will happily generate unaligned accesses. If
>> you disable dcache, these will trap.
> 
> What's that compiler flags we should be using to avoid that?

It's a combination of

   -mstrict-align

plus crossing fingers with lots of praying plus making sure that every 
code you call also follows -mstrict-align plus double-checking that you 
don't break the kernel booting ABI:

 
http://elixir.free-electrons.com/linux/v4.12-rc7/source/Documentation/arm64/booting.txt

In the booti case, disabling dcache seems to be legitimate. In the 
bootefi case however, it's not.

So you will also need to set CONFIG_EFI_LOADER to depend on 
!CONFIG_SYS_DCACHE_OFF which means you will want to convert 
CONFIG_SYS_DCACHE_OFF to Kconfig first :).

> The reason for this change is to have really small u-boot which fits to
> OCM without DDR to be able to do initial programming.

Yup, makes sense. I'm just slightly scared by the idea :).


Alex