linux-kernel - Re: [PATCH v2] powerpc 8xx: Loading kernels over 8Mbytes without CONFIG_PIN

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Message-ID: <1387319904.10013.482.camel@snotra.buserror.net>
Date:	Tue, 17 Dec 2013 16:38:24 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	leroy christophe <christophe.leroy@....fr>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] powerpc 8xx: Loading kernels over 8Mbytes without
 CONFIG_PIN_TLB

On Tue, 2013-12-17 at 06:54 +0100, leroy christophe wrote:
> Le 16/12/2013 23:57, Scott Wood a écrit :
> > On Wed, 2013-12-11 at 00:36 +0100, leroy christophe wrote:
> >> Le 11/12/2013 00:18, Scott Wood a écrit :
> >>> There wasn't previously an ifdef specifically around the setting of
> >>> SPRN_MD_CTR.  That's new.  There was an ifdef around the entire block,
> >>> which has gone away because you are now trying to map more than 8M
> >>> regardless of CONFIG_PIN_TLB, but that has nothing to do with whether
> >>> there should be an ifdef around SPRN_MD_CTR.
> >>>
> >>>
> >> Euh, ok, but then we have to fix it in the whole function, not only in
> >> this block. Do you think it is worth doing it ?
> > Fix what in the whole function?  I was asking what harm there would be
> > if you just remove all the CONFIG_PIN_TLB ifdefs except around the
> > actual RSV4I setting -- do we really care what value goes in MD_CTR for
> > the non-pinned case, as long as it's different for each entry?
> >
> >
> MD_CTR is decremented after each entry added.
> However, the function populates entry 28, then 29, then 30, then 31. At 
> the end MD_CTR has then value 30, ready to overide entry 30 then 29 then 
> 28 then 27 .....
> 
> So I will remove all the CONFIG_PIN_TLB, but I'll also have to fix the 
> value set in MD_CTR to start from 31, won't I ?

OK, so the answer is that we rely on autodecrement avoiding entries over
28 in the CONFIG_PIN_TLB case.  Leave the ifdefs, then.

> Do you have any comment/recommendation on my tentative v3 patch where I 
> have tried to implement based on the use of r7 as you recommended ?

I haven't reviewed it yet.

-Scott


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