On Mon, Aug 06, 2007 at 10:54:33PM +0200, Segher Boessenkool wrote:
> > Aha! Ok, now I understand the sorts of situations you're talking
> > about. By "not direct mapped", I thought you were talking about some
> > kind of access via address/data registers on some indirect bus
> > controller, rather than weird variations on endianness and
> > bit-swizzling.
> >
> > Hrm.. this is a property of how the flash is wired onto the bus,
> > rather than of the flash chips themselves, so I'm not entirely sure
> > where description of it belongs.
> >
> > Simplest option seems to me to add a property "endianness" or
> > "bit-swizzling" or something which can be defined to describe some odd
> > connections. If absent we'd default to direct mapping. Segher, is
> > that idea going to cause you to scream?
>
> No, that's fine with me. I would recommend either using a
> _good_ _descriptive_ name for such a property describing the
> swizzling, if this swizzling is common; or just put the whole
> bloody weirdo address permutation into some nice big array,
> something like
>
> address-permutation = <0 1 3 2 4 5 7 6 e f d c a b 9 8>;
Yes, I was contemplating something like that.
[snip]
> > So I left out ranges, on the grounds that there isn't actually
> > anything at present which will attempt to access flash partitions
> > "generically" as a device tree device.
>
> It looks good to me like this.
>
> In a real OF, the "register" access for the flash partition
> node would be handled by its parent node, which would know
> to do the direct-mapping thing (at least mapping it to _its_
> parent, which typically asks the nodes further up, etc.)
>
> For the kernel world, we should just document it in the binding.
>
> > I'm not sold on this approach, but I haven't heard you give a better
> > argument yet.
>
> I haven't heard or thought of anything better either. Using "ranges"
> is conceptually wrong, even ignoring the technical problems that come
> with it.
Why is "ranges" conceptually wrong?
To be honest this looks rather to me like another case where having
overlapping 'reg' and 'ranges' would actually make sense.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
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