linux-kernel - Re: [PATCH] UIO: only call pgprot

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Message-ID: <8bd0f97a0811050955k5fa31ccanc738b66348b83250@mail.gmail.com>
Date:	Wed, 5 Nov 2008 12:55:49 -0500
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Greg KH" <gregkh@...e.de>
Cc:	"Hans J. Koch" <hjk@...utronix.de>,
	"Mike Frysinger" <vapier@...too.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] UIO: only call pgprot_noncached if defined

On Wed, Nov 5, 2008 at 12:42, Greg KH wrote:
> On Wed, Nov 05, 2008 at 12:33:37PM -0500, Mike Frysinger wrote:
>> On Wed, Nov 5, 2008 at 11:33, Greg KH wrote:
>> > On Wed, Nov 05, 2008 at 12:36:11PM +0100, Hans J. Koch wrote:
>> >> There seem to be archs that cannot easily implement a sensible
>> >> pgprot_noncached() function, so we should merge this patch. UIO doesn't
>> >> compile on these archs right now.
>> >
>> > No, we should fix those arches to have that function at least NULLed
>> > out.  Isn't there only one, Blackfin?  Putting #ifdefs in .c files is
>> > not something we really want to do if at all possible.
>>
>> that was my question.  this function isnt documented.  if the hardware
>> doesnt support it, is the right thing really for the arch to lie to
>> drivers and not actually give back cached settings even though it
>> asked for non-cached ?
>
> Probably not, it sounds like the arch needs to be fixed :)

i'd agree, but we're dealing with reality here: we're talking no-mmu
and we can not do caching on a per-page basis while maintaining
anything resembling usable performance.
-mike
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