linux-kernel - Re: [RFC PATCH] MTD: atmel_nand: optimize read/write buffer functions

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Date:	Mon, 04 Jul 2011 15:02:47 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, hong.xu@...el.com,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH] MTD: atmel_nand: optimize read/write buffer	functions

Le 29/06/2011 15:31, Russell King - ARM Linux :
> On Wed, Jun 29, 2011 at 03:09:59PM +0200, Nicolas Ferre wrote:
>> Le 28/06/2011 16:59, Russell King - ARM Linux :
>>> I think you need to read Documentation/bus-virt-phys-mapping.txt,
>>> particularly the part after "NOTE NOTE NOTE".
>>>
>>> Dereferencing ioremap'd memory is not permitted.  That includes passing
>>> it to memcpy.  Even with a cast.
>>
>> So that means that I should use memcpy_fromio() even if the code if far
>> less optimized.
>>
>> Shouldn't I re-implement some kind of IO copying function to deal with
>> this IO memory so that I could take advantage of 8 words bursts?
> 
> You could improve the IO memcpy/set etc implementations, which are
> currently mostly unloved - I think that's a catch-22 which really needs
> solving.  They're not efficient because no one has taken the time to use
> them, and everyone's avoiding them because they're not very efficient.
> So, as no one's using them no one's motivated to improve them.

Ok, so I use them in my following patch.

And as a long-term exercise, I will try to have a look at those IO
memcpy/set functions for ARM...

Thanks for you advices, best regards,
-- 
Nicolas Ferre

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