linux-kernel - Re: [PATCH] NOMMU: use copy_*_user_page() in access_process

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Date:	Tue, 8 Dec 2009 19:27:36 -0500
From:	Mike Frysinger <vapier@...too.org>
To:	David Howells <dhowells@...hat.com>
Cc:	Jie Zhang <jie.zhang@...log.com>, uclinux-dev@...inux.org,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [PATCH] NOMMU: use copy_*_user_page() in access_process_vm()

On Tuesday 08 December 2009 09:19:27 David Howells wrote:
> Jie Zhang <jie.zhang@...log.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).

the Blackfin cpu currently does not have virtual memory support at all, so i 
imagine there's a bunch of things that'll need updating when that day comes

the new patch is of course fine; thanks
-mike

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