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Re: Time to make PCI_MSI default y ?

To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: Time to make PCI_MSI default y ?
From: Michael Ellerman <michael@ellerman.id.au>
Date: Wed, 25 Nov 2009 11:31:34 +1100
Cc: Ralf Baechle <ralf@linux-mips.org>, 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: <1259096952.16367.134.camel@pasglop>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1259030388.20596.5.camel@concordia> <20091124125309.GB5749@linux-mips.org> <1259096952.16367.134.camel@pasglop>
Reply-to: michael@ellerman.id.au
Sender: linux-mips-bounce@linux-mips.org
On Wed, 2009-11-25 at 08:09 +1100, Benjamin Herrenschmidt wrote:
> 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)

Oh yeah I forgot we could do that. So we could either do that, or add a
ARCH_MSI_DEFAULT and use that as the if condition. If people really
care.

cheers


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