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Re: [PATCHv4 02/11] pci: use weak functions for MSI arch-specific functi

To: Michael Ellerman <michael@ellerman.id.au>
Subject: Re: [PATCHv4 02/11] pci: use weak functions for MSI arch-specific functions
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date: Tue, 2 Jul 2013 07:30:37 +0200
Cc: Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org, Russell King <linux@arm.linux.org.uk>, Grant Likely <grant.likely@secretlab.ca>, Rob Herring <rob.herring@calxeda.com>, Thomas Gleixner <tglx@linutronix.de>, Jason Cooper <jason@lakedaemon.net>, Andrew Lunn <andrew@lunn.ch>, Gregory Clement <gregory.clement@free-electrons.com>, Lior Amsalem <alior@marvell.com>, linux-mips@linux-mips.org, linux-ia64@vger.kernel.org, Heiko Carstens <heiko.carstens@de.ibm.com>, Thierry Reding <thierry.reding@gmail.com>, Paul Mackerras <paulus@samba.org>, "H. Peter Anvin" <hpa@zytor.com>, sparclinux@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, Ingo Molnar <mingo@redhat.com>, Ezequiel Garcia <ezequiel.garcia@free-electrons.com>, Fenghua Yu <fenghua.yu@intel.com>, Chris Metcalf <cmetcalf@tilera.com>, linux-arm-kernel@lists.infradead.org, Tony Luck <tony.luck@intel.com>, Ralf Baechle <ralf@linux-mips.org>, Maen Suleiman <maen@marvell.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, linux390@de.ibm.com, linuxppc-dev@lists.ozlabs.org, "David S. Miller" <davem@davemloft.net>
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Dear Michael Ellerman,

On Tue, 02 Jul 2013 10:53:16 +1000, Michael Ellerman wrote:
> On Mon, 2013-07-01 at 15:42 +0200, Thomas Petazzoni wrote:
> > Until now, the MSI architecture-specific functions could be overloaded
> > using a fairly complex set of #define and compile-time
> > conditionals. In order to prepare for the introduction of the msi_chip
> > infrastructure, it is desirable to switch all those functions to use
> > the 'weak' mechanism. This commit converts all the architectures that
> > were overidding those MSI functions to use the new strategy.
> 
> The MSI code used to use weak functions, until we discovered they were
> being miscompiled on some toolchains (11df1f0). I assume these days
> we're confident they work correctly.

Hum, interesting. I see from your commit that gcc 4.3.2 was apparently
affected, and gcc 4.3.x is not /that/ old. Bjorn, what's your point of
view on this?

Another option would be to have architecture register some msi_arch_ops
structure, with a set of operations, which I believe is a pattern that
is more widespread in the kernel than weak functions.

Thoughts?

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

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