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

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Message-ID: <47FE46AC.5000901@ru.mvista.com>
Date:	Thu, 10 Apr 2008 20:56:12 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	linuxppc-dev@...abs.org, gregkh@...e.de,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	jgarzik@...ox.com, alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH 6/13] devres: implement managed iomap interface

Hello, I wrote:

>>>    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.

    Oops, I meant PCI drivers here, at least for the time being. And it looks 
like that was a false alarm. :-]

>> 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.

    I thought that pcim_iomap() used devm_ioremap() or something -- which of 
course turned to be wrong. devm_ioremap() alone is yet safe since there are no 
users for it amongst PPC 44x platform device drivers...

MBR, Sergei
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