netdev - Re: [PATCH] Change S390 anti-dependency to CONFIG_GENERIC

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Message-ID: <48F61EF8.20202@redhat.com>
Date:	Wed, 15 Oct 2008 12:48:56 -0400
From:	Chris Snook <csnook@...hat.com>
To:	David Miller <davem@...emloft.net>
CC:	afleming@...il.com, afleming@...escale.com, netdev@...r.kernel.org
Subject: Re: [PATCH] Change S390 anti-dependency to CONFIG_GENERIC_HARDIRQS
 dependency

David Miller wrote:
> From: Chris Snook <csnook@...hat.com>
> Date: Tue, 14 Oct 2008 20:07:55 -0400
> 
>> But then it will be much more of a pain to exclude the vast swath of
>> irrelevant code in the kernel tree from your builds on these exotic
>> architectures.  Have you ever built a kernel on s390?
> 
> That's totally irrelevant.
> 
> Does S390 have ethernet or ethernet-like devices?  If so, the someday
> it might in fact might want to use something like phylib instead of
> adding yet another implementation of programming a particular PHY
> chip.

Last I checked, s390 doesn't have any hardware that can't be shared 
between at least 64 guests.  The most Linux will ever control on that 
hardware is a software channel, be it a channel to a disk controller, 
network controller, or application-specific offload engine.  They don't 
really have NICs, more like a built-in router which can optionally fake 
layer 2 for the benefit of guests.

> So in fact, something like phylib should be possible to enable even on
> s390.
> 
> And this current situation means s390 builds get less coverage, making
> allmodconfig test builds (which the s390 folks are obviously doing
> since they hit this originally reported build failure) less
> useful than they could be.

Currently, allmodconfig on s390 is cheap, because there's a miniscule 
amount of device driver code that can be enabled in Kconfig.  If you 
enabled all those other drivers to build on s390, it would take *days* 
to complete an allmodconfig build natively or in an emulator.  Forcing 
people to use cross-compilers to get things done at a reasonable pace 
would mean treating s390 differently from other architectures in 
multi-platform build systems, and would probably have the effect that 
nobody outside of IBM would do any significant build testing on that 
architecture.

> I would even be happy to make it such that SBUS drivers can be
> enabled for test building on x86, and in fact right now in
> Linus's tree that's very close to doable.

I have no objection to that.  I have MIPS to burn on my x86 boxes.  s390 
MIPS cost a few orders of magnitude more.

-- Chris
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