[PATCH] Revert "spl: Drop bd_info in the data section"

[Alex G.]

Hi Simon

On 4/8/21 6:55 PM, Simon Glass wrote:
> Hi Alexandru,
> 
> On Fri, 9 Apr 2021 at 04:56, Alexandru Gagniuc <mr.nuke.me at gmail.com> wrote:
>>
>> This reverts commit 38d6b7ebdaee3e0e8426ef1b9df88bdce8ae2e75.
>>
>> struct global_data contains a pointer to the bd_info structure. This
>> pointer was populated spl_set_bd() to a pre-allocated bd_info in the
>> ".data" section. The referenced commit replaced this mechanism to one
>> that uses malloc(). That new mechanism is only used if SPL_ALLOC_BD=y.
>> which very few boards do.
>>
>> The result is that (struct global_data)->bd is NULL in SPL on most
>> platforms. This breaks falcon mode, since arch_fixup_fdt() tries to
>> access (struct global_data)->bd and set the "/memory" node in the
>> devicetree. The result is that the "/memory" node contains garbage
>> values, causing linux to panic() as it sets up the page table.
>>
>> Instead of trying to fix the mess, potentially causing other issues,
>> revert to the code that worked, while this change is reworked.
> 
> The goal here is to drop a feature that few boards use and reduce
> memory usage in SPL. It has been in place for two releases now.
> 
> If Falcon mode needs it, perhaps you could add an 'imply' in the
> Kconfig for that feature? Is there one? Or perhaps
> CONFIG_ARCH_FIXUP_FDT_MEMORY ?
> 
> One option would be to return an error in arch_fixup_fdt(). In
> general, fixups make things tricky because there is no way to
> determine when they are used but at least this one has a CONFIG.
> 

The argument that this has been in place for two releases is incorrect. 
Commit 38d6b7ebdaee3e0e8426ef1b9df88bdce8ae2e75 was only introduced with 
the v2021.04 release. It definitely was not in 2021.01. It's only in the 
last release, which is four days old t the time of this writing.

Although I was able to find one example, the reality is that we don't 
know the full extent of the breakage. The prudent thing at this point is 
to revert.

The knowledge of how to init the platform is in the devicetree and code. 
Why should kconfig also be involved in storing this knowledge? By this 
model, as the number of boards increases without bounds, every "if" 
predicate tends to be Kconfig driven. That is not maintainable, and why 
I think the original change --and the proposed fixes-- are broken by design.

Furthermore, I'm happy to discuss what to do about Falcon mode, and if 
we should kill it entirely (I have an alternative proposal).  But we 
shouldn't have that discussion in a manner holding my platform hostage. 
To be fair to you, I don't think reverting a 64-byte savings in .data 
will hold your platform hostage either.

Alex