linux-kernel - Re: [PATCH 6/13] devres: implement managed iomap interface

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Date:	Tue, 08 Apr 2008 18:55:13 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	jgarzik@...ox.com, gregkh@...e.de, alan@...rguk.ukuu.org.uk,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	linuxppc-dev@...abs.org
Subject: Re: [PATCH 6/13] devres: implement managed iomap interface

Tejun Heo wrote:

>>    A very late comment but nevertheless... :-)

> Better late than never.

    :-)

>>    Those functions are going to break on 32-bit platforms with 
>> extended physical address (well, that's starting with Pentiums which 
>> had 36-bit PAE :-) AND devices mapped beyond 4 GB (e.g. PowerPC 44x).  
>> You should have used resource_size_t for the 'offset' parameter. As 
>> this most probably means that libata is broken on such platforms, I'm 
>> going to submit a patch...

    It's broken with drivers using MMIO, I meant to say.

> Yeah, right please go ahead.  But I wonder whether any BIOS was actually 
> crazy enough to map mmio region above 4G on 32bit machine.

    This is a *hardware* mapping on some non-x86 platforms (like PPC 44x or 
MIPS Alchemy). The arch/ppc/ and arch/mips/ kernels have special hooks called 
from ioremap() which help create an illusion that the PCI memory space on such 
platforms (not only it) is mapped below 4 GB; arch/powerpc/ kernel doesn't do 
this anymore -- hence this newly encountered issue.

WBR, Sergei
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