Re: [PATCH] drm/i915: swizzling support for snb/ivb

[Daniel Vetter <daniel@ffwll.ch>]

On Sat, Feb 04, 2012 at 07:13:41PM -0800, Ben Widawsky wrote:
> On 02/02/12 00:40, Daniel Vetter wrote:
> >On Wed, Feb 01, 2012 at 09:30:57PM -0800, Ben Widawsky wrote:
> >[...]
> >>I'd also say it's not a bad idea to elaborate the assumption that we
> >>never have less than 256MB of memory WARN_ON(dimm_c0 + dimm_c1 == 0).
> >
> >I'm pretty sure that we can't boot with 0mb of ram ;-) The other thing is
> >that swizzling is a pure preformance optimization - if we enable it on
> >setup where it's not required we'll only annoy the memory controller with
> >less efficient access patterns.
> 
> What I meant was, this value is still 0 in say, a system with 2
> 128MB DIMMs.

Well, I have a feeling that 256mb is the smallest size for a ddr3 dimm.
But I'm a bit too lazy to check that (and frankly wouldn't know where).
Furthermore swizzling on gen6+ is afaics just a performance thing and
should never affect correctness, so even if 128mb dimms exist I think we
can just not care - performance isn't gonna be stellar anyway ;-)
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48