Date: Tue, 3 Jun 2008 15:49:08 -0500
From: Nathan Lynch <ntl@pobox.com>
To: Hannes Hering <hannes.hering@linux.vnet.ibm.com>
Cc: jeff@garzik.org, tklein@de.ibm.com, themann@de.ibm.com,
       netdev@vger.kernel.org, linux-kernel@vger.kernel.org, raisch@de.ibm.com,
       ossrosch@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org,
       ossthema@de.ibm.com, Badari Pulavarty <pbadari@us.ibm.com>
Subject: Re: [PATCH 2/3] [2.6.26] ehea: Add dependency to Kconfig
Message-ID: <20080603204908.GB7475@localdomain>
References: <200805071443.20192.hannes.hering@linux.vnet.ibm.com>
 <20080528164405.GA4836@localdomain>
 <200806031007.40162.hannes.hering@linux.vnet.ibm.com>
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Hannes Hering wrote:
> 
> On Wednesday 28 May 2008 18:44:05 Nathan Lynch wrote:
> > 
> > Hannes Hering wrote:
> > > The new ehea memory hot plug implementation depends on MEMORY_HOTPLUG.
> > > 
> > > Signed-off-by: Hannes Hering <hering2@de.ibm.com>
> > > ---
> > > 
> > > diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> > > index f90a86b..181cd86 100644
> > > --- a/drivers/net/Kconfig
> > > +++ b/drivers/net/Kconfig
> > > @@ -2440,7 +2440,7 @@ config CHELSIO_T3
> > >  
> > >  config EHEA
> > >  	tristate "eHEA Ethernet support"
> > > -	depends on IBMEBUS && INET && SPARSEMEM
> > > +	depends on IBMEBUS && INET && SPARSEMEM && MEMORY_HOTPLUG
> > >  	select INET_LRO
> > >  	---help---
> > >  	  This driver supports the IBM pSeries eHEA ethernet adapter.
> > 
> > I disagree with this change.
> > 
> > It makes it impossible to build the ehea driver without memory hotplug
> > enabled.  Presumably, this commit was intended to work around a build
> > break of this sort (with EHEA=m and MEMORY_HOTPLUG=n):
> > 
> > drivers/net/ehea/ehea_qmr.c: In function 'ehea_create_busmap':
> > drivers/net/ehea/ehea_qmr.c:635: error: implicit declaration of function 'walk_memory_resource'
> > 
> > (some indication of this should have been in the commit message, btw)
> > 
> > I think this was the wrong way to fix the issue.  EHEA=m and
> > MEMORY_HOTPLUG=n is a valid configuration for machines I test.
> > 
> > Any thoughts on the following, which makes walk_memory_resource()
> > available regardless of MEMORY_HOTPLUG's setting?  I've tested it on a
> > JS22 (Power6 blade).
>
> I agree that the ehea cannot be built without MEMORY_HOTPLUG. The
> problem is the fact that the ppc walk_memory_resource declaration is
> in the scope of MEMORY_HOTPLUG. At the moment I don't have complete
> overview if the move of the code as you propose in your patch has
> any side effects. We probably need to talk to Badari who provided
> the walk_memory_resource code. We can also just throw it onto one of
> our boxes to see what happens. ;)

I would certainly appreciate any additional testing.

You wrote the ehea code that uses walk_memory_resource, so I was
hoping you could speak to whether ehea needs that interface when
CONFIG_MEMORY_HOTPLUG=n.  Or maybe there should be a no-op version of
walk_memory_resource for that case?  And what about the
arch-independent version in kernel/resource.c?  Badari?

It would be nice to get this resolved for 2.6.26 -- this new
dependency causes working 2.6.25 configs to effectively fail (by
deselecting CONFIG_EHEA during make oldconfig).
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