Re: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous Memory Allocator added

[Daniel Stone <daniels@collabora.com>]

Hi,

On Tue, Jun 14, 2011 at 06:03:00PM +0200, Arnd Bergmann wrote:
> On Tuesday 14 June 2011, Michal Nazarewicz wrote:
> > On Tue, 14 Jun 2011 15:49:29 +0200, Arnd Bergmann <arnd@arndb.de> wrote:
> > > Please explain the exact requirements that lead you to defining multiple
> > > contexts.
> > 
> > Some devices may have access only to some banks of memory.  Some devices
> > may use different banks of memory for different purposes.
> 
> For all I know, that is something that is only true for a few very special
> Samsung devices, and is completely unrelated of the need for contiguous
> allocations, so this approach becomes pointless as soon as the next
> generation of that chip grows an IOMMU, where we don't handle the special
> bank attributes. Also, the way I understood the situation for the Samsung
> SoC during the Budapest discussion, it's only a performance hack, not a
> functional requirement, unless you count '1080p playback' as a functional
> requirement.

Hm, I think that was something similar but not quite the same: talking
about having allocations split to lie between two banks of RAM to
maximise the read/write speed for performance reasons.  That's something
that can be handled in the allocator, rather than an API constraint, as
this is.

Not that I know of any hardware which is limited as such, but eh.

Cheers,
Daniel