[U-Boot] [U-Boot-DM] early_malloc() vs. enable_caches()

[Graeme Russ]

Hi Thomas,

On Sun, Jul 29, 2012 at 11:19 PM, Tomas Hlavacek <tmshlvck at gmail.com> wrote:
> Hi Graeme,
>
> On Sun, Jul 29, 2012 at 12:53 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
>
>> Not exactly on-topic, but I really hope that everything is wrapped so a
>> simple call to malloc() will work pre-relocation. Of course, everything you
>> malloc pre-relocation will have to be re-malloc'd and relocated after
>> relocation. Point is, early malloc should not be restricted to the driver
>> framework
>
> Yes. Actually my intention is to create a wrapper for switching from
> early_malloc()
> to dlmalloc() based on gd->flags. I am going to do that when the concept of
> early_malloc() is finished.

Yes, I saw that patch.

>> 1) Low-level CPU init
>> 2) 'Cache-As-RAM' init
>> 3) Global Data init
>> 4) Pre-console buffer init
>> 5) Early malloc() init
>> 6) Console init
>> 7) ...blah, blah, blah...
>> 8) SDRAM init
>> 9) Relocate Global Data
>> 10) malloc() init
>> 11) 'Disable' early malloc (i.e. malloc() now allocates from SDRAM)
>> 12) Relocate from early_malloc_pool to malloc_pool [1]
>> 13) enable_caches()
>>
>> [1] I'm thinking possibly compile-time registered hooks...
>>
>>> Does it make sense? It actually boils down to one fundamental question:
>>> When I have not-rellocated data locked in cache-lines, do I loose them once
>>> enable_caches() is called?
>>
>> I believe that yes, as soon as you enable caching, everything already in
>> cache (gd, pre-console buffer, early malloc pool etc) is as good as gone
>
> Thanks for explanation!
>
> We have reconsidered relocation of DM structures. Perhaps we are going to
> keep the structures on early_heap (in copied GD) and we are going to convert

You lost me here - early_heap is in cache like ealry GD but then you talk
about copied GD which is in SDRAM...

> pointers inside our structures and copy data after actual relocation when the
> dlmalloc and caches are up and running. We think that this might be fastest
> approach.

My fear is that early_heap will end up being restricted to be usable only
be the driver framework. Perhaps you could:
1) SDRAM Init
2) Relocate GD
3) Temporarily relocate ealry heap - store offset in GD
4) enable_caches()
5) malloc() init
6) Permanently relocate early heap into malloc heap

Faster, but a lot of mucking around. And drivers are broken between steps
3 and 6 (but that should not be too much of a problem)

Regards,

Graeme