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

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Message-Id: <59A939C7-75AF-4C0F-8199-4C31D174AEA9@kernel.crashing.org>
Date:	Thu, 10 Apr 2008 12:44:12 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Tejun Heo <htejun@...il.com>, linux-ide@...r.kernel.org,
	gregkh@...e.de, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, jgarzik@...ox.com,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH 6/13] devres: implement managed iomap interface


On Apr 10, 2008, at 11:56 AM, Sergei Shtylyov wrote:
> 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...

but there is no reason not to make it work properly.  For example I  
believe libata uses devm_* and the fsl SATA driver (non-PCI) will need  
to work in cases similar to the 44x.

- k
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