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Message-ID: <16215.14133.352143.660688@nanango.paulus.ozlabs.org>
Date: Thu, 4 Sep 2003 22:59:33 +1000 (EST)
From: Paul Mackerras <paulus@samba.org>
To: Russell King <rmk@arm.linux.org.uk>
Cc: "David S. Miller" <davem@redhat.com>, hch@lst.de, torvalds@transmeta.com,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix ppc ioremap prototype
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Russell King writes:

> Using the high flag bits probably isn't a good idea for two reasons:
> 
> 1. We already use bit 31 to indicate the busy status:
> 
>    #define IORESOURCE_BUSY         0x80000000      /* Driver has marked this resource busy */
> 
>    However, it looks like bits 27 to 17 are currently unused.

Using some flag bits would work but it seems like a bit of a kludge.
Maybe the struct resource needs to have a pointer to the struct device
which owns it?  Or maybe just a `sysdata' field?

> 2. The resource tree won't know about the upper bits or whatever sitting
>    in flags, and as such identical addresses on two different buses will
>    clash.
> 
> Resource start,end needs to be some unique quantity no matter which (PCI)
> bus you are on.

They are non-overlapping for PCI buses in the same domain.  Perhaps
the sensible thing is to have a separate resource tree for each PCI
domain (actually two trees, for I/O and memory space), and have them
contain bus addresses rather than physical addresses.  I don't know if
the generic iomem_resource and ioport_resource are still useful if we
do that.

Paul.
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