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

[Marek Vasut <marek.vasut@gmail.com>]

Dear Graeme Russ,

> Hi Thomas,
> 
> P.S. I dropped the DM list...
> 
> It took a couple of other emails to get what is going on here...
> 
> On 07/29/2012 01:46 AM, Tomas Hlavacek wrote:
> > Hello!
> > 
> > I am working on early_malloc() for U-Boot Driver Model (this malloc is
> > going to serve for internal DM structures during early init and it has
> > it's minimalistic heap in global data).
> 
> 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
> 
> > My question is how to correctly switch from early allocator to full-scale
> > malloc and when to enable caches.
> > 
> > The current state (on ARM) is:
> > 1) gd = id;
> > 3) enable_caches();
> > 3) mem_malloc_init();
> > 
> > Proposed sequence for mallocator (in order no to loose any data from old
> > and not-relocated part of GD):
> > 
> > 1) gd_old = gd;
> > 2) gd = id;
> > 3) mem_malloc_init();
> > 4) relocation of DM structures
> > 5) early_malloc_disab()
> > 6) enable_caches();
> 
> I'm thinking:
> 
> 1) Low-level CPU init
> 2) 'Cache-As-RAM' init
> 3) Global Data init
> 4) Pre-console buffer init

Buffer?

> 5) Early malloc() init
> 6) Console init

You don't need console here ... probably, on some systems.

> 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...

Gurr ... you mean like INIT-something framework?

> > 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

Right ... that's why now it's copied to a safe location alongside other GD 
(global data)

> Regards,
> 
> Graeme

Best regards,
Marek Vasut