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From: David Gibson <david@gibson.dropbear.id.au>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: linuxppc-dev@ozlabs.org
Subject: Re: [PATCH 2/6] PowerPC 440EPx: Sequoia DTS
Date: Fri, 10 Aug 2007 11:07:23 +1000	[thread overview]
Message-ID: <20070810010723.GB17370@localhost.localdomain> (raw)
In-Reply-To: <019ae19815eb3301065ba732e3e72f44@kernel.crashing.org>

On Thu, Aug 09, 2007 at 09:53:41PM +0200, Segher Boessenkool wrote:
> >>>> 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
> >> "flash bus", they are "sub-devices" of their parent.
> >
> > Well, yes, but nonetheless the partitions show up as part of the
> > overall physical address space.  How do you encode that other than in
> > 'ranges'?
> 
> All that address space shows up in the flash node already.  To
> access the partitions you have to go via that "master" node
> anyway (some commands have to be sent to address 0 on the flash,
> or similar).

Hrm, I suppose.  Although for read-only access that's not relevant.

> It is a very nice feature to not only be able to translate addresses
> "up" the device tree, but also "down".

I don't follow, sorry.

> Also, it mimics reality, just like a good OF citizen should:
> those partitions aren't actually devices at all, so they
> certainly shouldn't be assigned a part of the host address
> space.

Hrm.  I'm not entirely convinced that the distinction between
"actually a device" and "not actually a device" is really as clear cut
as you imply.

> >>> 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.
> >
> > Why not?  After all, the physical address ranges of the flash
> > partitions really do overlap with that of the flash device as a whole.
> 
> They don't overlap, a partition is a proper subset of the flash.

A proper subset is a form of overlapping (indeed cases of being a
proper subset form a proper subset of cases of overlapping, to be
gratuitously meta-set-theoretic).

> Which as usual is shown as "reg" in the child node and #a,#s in
> the parent node.

That in no way encodes that the child addresses are a subset of the
parent address space.  Instead #a and #s establish a new, separate
address space for the children, and without 'ranges', there's no
information about any sort of connection, overlapping, proper-subset
or otherwise, with the parent address space.

-- 
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_!
http://www.ozlabs.org/~dgibson

  reply	other threads:[~2007-08-10  1:07 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-07-30 15:06 [PATCH 2/6] PowerPC 440EPx: Sequoia DTS Valentine Barshak
2007-08-01  2:08 ` David Gibson
2007-08-01  4:57   ` Segher Boessenkool
2007-08-01  5:04     ` David Gibson
2007-08-01  5:47       ` David Gibson
2007-08-02 15:23         ` Sergei Shtylyov
2007-08-03  3:13           ` David Gibson
2007-08-03 15:47             ` Sergei Shtylyov
2007-08-06  4:21               ` David Gibson
2007-08-06 18:37                 ` Sergei Shtylyov
2007-08-06 21:03                   ` Segher Boessenkool
2007-08-06 22:15                   ` Benjamin Herrenschmidt
2007-08-06 23:09                     ` Segher Boessenkool
2007-08-07  3:29                     ` David Gibson
2007-08-07  3:28                   ` David Gibson
2007-08-07 15:43                     ` Scott Wood
2007-08-07 17:01                       ` Segher Boessenkool
2007-08-07 16:43                     ` Segher Boessenkool
2007-08-08  0:35                       ` David Gibson
2007-08-19 12:59                     ` Sergei Shtylyov
2007-08-06 20:54                 ` Segher Boessenkool
2007-08-07  4:12                   ` David Gibson
2007-08-07 16:51                     ` Segher Boessenkool
2007-08-08  1:13                       ` David Gibson
2007-08-09 19:53                         ` Segher Boessenkool
2007-08-10  1:07                           ` David Gibson [this message]
2007-08-10 20:48                             ` Segher Boessenkool
2007-08-24 19:10                       ` Sergei Shtylyov
2007-08-24 20:43                         ` Segher Boessenkool
2007-08-06 20:35               ` Segher Boessenkool
2007-08-07  4:09                 ` David Gibson
2007-08-07 16:58                   ` Segher Boessenkool
2007-08-08  0:48                     ` David Gibson
2007-08-06 20:20             ` Segher Boessenkool
2007-08-07  3:35               ` David Gibson
2007-08-06 20:12           ` Segher Boessenkool
2007-08-02 20:18         ` Josh Boyer
2007-08-03  0:49           ` David Gibson
2007-08-03 16:29         ` Sergei Shtylyov
2007-08-06  4:31           ` David Gibson
2007-08-06 20:55             ` Segher Boessenkool
2007-08-06 20:41           ` Segher Boessenkool
2007-08-06 19:59         ` Segher Boessenkool
2007-08-07  3:41           ` David Gibson
2007-08-07 16:33             ` Segher Boessenkool
2007-08-08  1:51               ` David Gibson
2007-08-09 20:00                 ` Segher Boessenkool
2007-08-10  1:11                   ` David Gibson
2007-08-02 20:16       ` Josh Boyer
2007-08-01 14:13   ` Valentine Barshak
2007-08-02  1:00     ` David Gibson
2007-08-02 20:15   ` Josh Boyer
2007-08-06 20:15     ` Segher Boessenkool
2007-08-07  4:11       ` David Gibson

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