Message-ID: <4B1E62ED.1060304@analog.com>
Date: Tue, 8 Dec 2009 22:30:05 +0800
From: Jie Zhang <jie.zhang@analog.com>
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To: David Howells <dhowells@redhat.com>
CC: Mike Frysinger <vapier@gentoo.org>, uclinux-dev@uclinux.org,
       David McCullough <davidm@snapgear.com>, Greg Ungerer <gerg@uclinux.org>,
       Paul Mundt <lethal@linux-sh.org>, linux-kernel@vger.kernel.org,
       uclinux-dist-devel@blackfin.uclinux.org
Subject: Re: [PATCH] NOMMU: use copy_*_user_page() in access_process_vm()
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On 12/08/2009 10:19 PM, David Howells wrote:
> Jie Zhang<jie.zhang@analog.com>  wrote:
>
>> I agree on using 0 instead of NULL. But for !MMU, I think, vaddr is always as
>> same as addr. So we don't need to pass it?
>
> FRV flushes the vaddr because in MMU mode the cache flush instructions take
> virtual addresses, so if we pass addr as vaddr, I can use the same cache flush
> code for both modes.  I suspect it makes little difference to the amount of
> code if we pass that rather than 0, as the value is already computed, and
> either way, it's going to take one instruction to set up the argument.
>
> Note that Blackfin assumes that it may use the dst address for flushing - an
> assumption that isn't valid in MMU mode with a VIVT cache (which I presume
> Blackfin isn't, but other CPUs are).
>
Thanks for your explanation. Now I understand why passing add as vaddr 
is better.


Jie
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