linux-kernel - Re: [PATCH v2] ARM: mmp: bring up pxa988 with device tree support

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Message-Id: <201306172334.05626.arnd@arndb.de>
Date:	Mon, 17 Jun 2013 23:34:05 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Chao Xie <xiechao.mail@...il.com>
Cc:	Neil Zhang <zhangwm@...vell.com>, Chao Xie <cxie4@...vell.com>,
	"haojian.zhuang@...il.com" <haojian.zhuang@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Russell King - ARM Linux" <linux@....linux.org.uk>
Subject: Re: [PATCH v2] ARM: mmp: bring up pxa988 with device tree support

On Monday 17 June 2013, Chao Xie wrote:
> On Fri, Jun 14, 2013 at 8:56 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Friday 14 June 2013 17:15:33 Chao Xie wrote:
> >> On Mon, Jun 10, 2013 at 4:35 PM, Arnd Bergmann <arnd@...db.de> wrote:
> >
> >> > I guess that is a problem we have on other platforms as well, we should
> >> > find a generic solution for that. It would be nice to reserve a page
> >> > in "fixmap" and have common code map the SCU page into that.
> >> >
> >>
> >> So you mean that reserve a page in arch/arm/asm/include/fixmap.h?
> >
> > Yes.
> >
> >> This reserve will depend on the cpu type beacuse only A9 will have SCU part.
> >
> > I think A5 and ARM11MPCore as well.
> >
> >> I do not know that in fixmap, the #ifdef is acceptable or not.
> >
> > Yes, it is. We don't really use fixmap on ARM for anything other than
> > kmap_atomic at the moment. Please have a look at the powerpc and x86
> > implementations.
> >
> >> For the common code to map the SCU page, where do you suggest to put it?
> >
> > arch/arm/kernel/smp_scu.c.
> >
> I think smp_scu.c may not be good place to put the mapping for SCU page.
> As you know that the fix map will make use of the mapping that set up
> by vector page.
> It will make use of top_pmd, and some APIs only provided under arch/arm/mm/.
> For example
> get_mem_type: for the pgprot for MT_DEVICE
> set_top_pte:
> Is that possible to add a file fixmap.c under arch/arm/mm/? It can
> including all the fix mapping
> except highmem. So SCU is one of it.

It's up to Russell, and he probably has an idea where this should be
going.

Russell, do you think using a fixmap page for the SCU makes sense?
I'm looking for a method to consolidate the various methods of
doing early mappings of the SCU for device tree based platforms.
Where do you think that should be implemented?

	Arnd
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