Subject: Re: [PATCH] powerpc:Fix rheap alignment problem

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 03 Jul 2006 21:08:49 +1000

On Sun, 2006-07-02 at 08:18 +0300, Pantelis Antoniou wrote:
> On Sunday 02 July 2006 06:54, Rune Torgersen wrote:
> > From: Pantelis Antoniou
> > Sent: Sat 7/1/2006 9:50 AM
> > >Since genalloc is the blessed linux thing it might be best to use that & remove
> > >rheap completely. Oh well...
> > 
> > Two problems with genalloc that I can see (for CPM programming):
> > 1) (minor) Does not have a way to specify alignment (genalloc does it for you)
> > 2) (major problerm, at least for me) Does not have a way to allocate a specified address in the pool.
> > 
> > 2 is needed esp when programming MCC drivers, since a lot of the datastructures must be in DP RAM _and_ be in a specific spot. And if you cannot tell the allocator that I am using a specific address, then the allocator might very well give somebody else that portion of RAM. The only solution without a fixed allocator is to allocate ALL memory in the DP RAM and use your own allocator. 
> > 
> 
> Yeah, that too.
> 
> Too bad there are no main tree drivers like that, but they do exist.
> 
> One could conceivably hack genalloc to do that, but will end up with
> something complex too.
> 
> BTW, there are other uEngine based architectures with similar alignment
> requirements.
> 
> So in conclusion, for the in-tree drivers genalloc is sufficient as an cpm memory allocator.
> For some out of tree drivers, it is not.

Sounds like a good enough justification to keep rheap for now then.

Ben.