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Re: Time to make PCI_MSI default y ?

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: Time to make PCI_MSI default y ?
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Wed, 25 Nov 2009 08:09:12 +1100
Cc: Michael Ellerman <michael@ellerman.id.au>, linux-pci <linux-pci@vger.kernel.org>, linux@arm.linux.org.uk, "tony.luck" <tony.luck@intel.com>, fenghua.yu@intel.com, "David S.Miller" <davem@davemloft.net>, Thomas Gleixner <tglx@linutronix.de>, mingo@redhat.com, Peter Anvin <hpa@zytor.com>, linux-mips@linux-mips.org, David Daney <ddaney@caviumnetworks.com>
In-reply-to: <20091124125309.GB5749@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
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On Tue, 2009-11-24 at 12:53 +0000, Ralf Baechle wrote:
> On Tue, Nov 24, 2009 at 01:39:48PM +1100, Michael Ellerman wrote:
> 
> > Having just hit a build-break caused by a distro building with
> > PCI_MSI=n, I set out to make it default y for powerpc. Unfortunately
> > that's not possible, because it's in drivers/pci/Kconfig.
> > 
> > So is it time to make it default y for everyone? It seems to me having
> > it off is more likely to cause problems than having it on these days,
> > though I'm not sure if that is true for all archs.
> > 
> > An arch that really didn't want it default y could conditionally select
> > ARCH_SUPPORTS_MSI, like x86 does already.
> 
> On MIPS the age of MSI only recently started; once single platform (Cavium)
> out of all the many uses it.  Cavium does a "select ARCH_SUPPORTS_MSI" but
> not "select PCI_MSI" because not all platform variants actually have PCI.
> 
> We should  not give a user a chance to select something wrong in kconfig
> thus automatically as many options for a platform as possible is a good
> thing - after all the kconfig dialog for any given platfrom has become
> painfully long.  And we really should have to avoid users having to know
> that the Frobnic 2000 they're trying to upgrade the kernel for requires
> MSI to work ...

Still... select has nasty issues. I think default y is fine here. For
platforms that don't need it, make sure their defconfigs don't have it
set...

Or maybe default y if (X86 || PPC)

Cheers,
Ben.



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