linux-kernel - Re: [PATCH 2/4] PCI: Support multiple MSI

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Date:	Mon, 07 Jul 2008 13:56:52 +1000
From:	Michael Ellerman <michael@...erman.id.au>
To:	Matthew Wilcox <matthew@....cx>
Cc:	linux-pci@...r.kernel.org, kaneshige.kenji@...fujitsu.com,
	mingo@...e.hu, tglx@...utronix.de, davem@...emloft.net,
	dan.j.williams@...el.com, Martine.Silbermann@...com,
	benh@...nel.crashing.org, linux-kernel@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH 2/4] PCI: Support multiple MSI

On Sun, 2008-07-06 at 20:45 -0600, Matthew Wilcox wrote:
> On Mon, Jul 07, 2008 at 12:05:25PM +1000, Michael Ellerman wrote:
> > On Sat, 2008-07-05 at 09:34 -0400, Matthew Wilcox wrote:
> > > Add the new API pci_enable_msi_block() to allow drivers to
> > > request multiple MSIs.  Reimplement pci_enable_msi in terms
> > > of pci_enable_msi_block.  Add a default implementation of
> > > arch_setup_msi_block() that only allows one MSI to be requested.
> > 
> > I don't think you need arch_setup_msi_block() at all.
> > 
> > We already have an arch hook that takes a number of irqs, it's
> > arch_setup_msi_irqs(), plural. It also has the type passed to it (MSI or
> > MSI-X), so it can decide if it needs to allocate the irq numbers
> > contiguously.
> > 
> > Or am I missing something?
> 
> I suppose I should audit the current implementors of arch_setup_msi_irqs
> (er, maybe that's just you?) to be sure that there's no assumption that
> MSI -> asked for one.  

Yeah I think it's just us.

But there's also the default implementation, which will happily use the
singular arch hook to setup multiple MSIs without any constraint on the
irq numbers - which will break.

So I think you want to make the default arch_msi_check_device() return
an error if you ask for MSI & nvec > 1. Then on powerpc we'll probably
add the same check to our version (at least until we can test it), but
on x86 you can let MSI & nvec > 1 pass.

> I'll look into doing it your way tomorrow (my timezone ;-)

Sure, although that'll be today in my timezone :D

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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