linux-kernel - Re: [PATCH v3 2/2] i2c: xiic: Use 32bit accesses only

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Date:	Wed, 23 Feb 2011 10:37:31 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Arnd Bergmann <arnd@...db.de>
CC:	devicetree-discuss@...ts.ozlabs.org,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-i2c@...r.kernel.org, john.williams@...alogix.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] i2c: xiic: Use 32bit accesses only

Arnd Bergmann wrote:
> On Wednesday 23 February 2011 09:08:47 Michal Simek wrote:
>> Grant Likely wrote:
>>> On Tue, Feb 22, 2011 at 10:49 AM, Michal Simek <monstr@...str.eu> wrote:
>>>> i2c driver is used for LE/BE that's why is useful to use
>>>> 32bit accesses. Then it is not necessary to solve any
>>>> endian issues.
>>> Are you sure?  I would expect the BE version needs to use
>>> io{read,write}32be variants of the accessors.  What platforms have you
>>> tested on?
>> iowrite32 is the same with iowrite32be for Microblaze.
>> I have no problem to change it to iowrite32be if you like.
>>
>> I have tested it on microblaze big and little endian platforms.
> 
> I think what Grant was saying is that iowrite32 being the same as
> iowrite32be is a bug, because iowrite32 is documented to be little-endian.

Can you pointed me to that documentation?

> 
> This is probably fine as long as you don't have any PCI devices,
> but if you ever get PCI support, it won't work.

Microblaze have PCI support but I don't have the board for testing.

> 
> Also, it heavily confuses other developers such as Grant and me
> if one architecture defines things to mean something completely
> different from the other architectures.

As I see will be good to review microblaze io.h and use generic one.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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