Subject: Re: [PATCH 2/6] PowerPC 440EPx: Sequoia DTS

From: Sergei Shtylyov <[email-masked]>
Date: Fri, 24 Aug 2007 23:10:36 +0400

Segher Boessenkool wrote:

>>>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.

> Let's not define this until we need it though :-)

    Let's ot even think of it, since this will end up in a "catch all" driver, 
and yet this may be not enough when the flash doesn't support 8-but R/W, for 
example (I've already quoted it...

>>>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?

> The flash partitions aren't separate devices sitting on a

    Yeah, that's why I decided not to go that from the very start... though 
wait: I didn't do this simply because they'renot devices.
That lead me to interesting question: do device tree have something for the 
disk partitions?

> "flash bus", they are "sub-devices" of their parent.

    They're quite an abstaction of a device -- althogh Linux treats them as 
separate devices indeed.

>>To be honest this looks rather to me like another case where having
>>overlapping 'reg' and 'ranges' would actually make sense.

> It never makes sense.  You should give the "master" device
> the full "reg" range it covers, and have it define its own
> address space; "sub-devices" can carve out their little hunk
> from that.  You don't want more than one device owning the
> same address range in the same address space.

    So, no "ranges" prop in MTD node is necessary? Phew... :-)

> Segher

WBR, Sergei