linux-kernel - Re: [3/5] 2.6.21-rc4: known regressions (v2)

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Message-Id: <200704020938.40482.bjorn.helgaas@hp.com>
Date:	Mon, 2 Apr 2007 09:38:40 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	linux-pci@...ey.karlin.mff.cuni.cz
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Thomas Meyer" <thomas@...3r.de>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Len Brown" <lenb@...nel.org>
Subject: Re: [3/5] 2.6.21-rc4: known regressions (v2)

On Monday 26 March 2007 21:29, Eric W. Biederman wrote:
> "Luck, Tony" <tony.luck@...el.com> writes:
> 
> >> What I'm proposing we do is move the irq allocation code out of
> >> pci_enable_device and the irq freeing code out of pci_disable_device
> >> in the future.
> >
> > Sounds rational ... in a world that wasn't dominated by PCI it would
> > seem to be the logical approach (since the irq code would have much
> > more utility independent of the PCI code).
> 
> Right.  We can even do this earlier in the pci code.  Just doing this
> on demand when the device driver needs it is problematic.  As devices
> drivers like to keep the requested over a pci_disable_device pci_enable_device
> pair.
> 
> The big practical issue is that we will like wind up allocating an irq
> number to all usable irqs on ia64.  Which means we will like need many
> more irq numbers...  Although I guess if we keep it at the pci layer
> we should be fairly safe.

The main reason we wait until pci_enable_device() to allocate an
IRQ number is that ia64 currently only has about 180 device vectors,
and there are machines with more PCI slots than that.

I also think it's nice that we don't do anything with a device until
we have a driver to claim it.  But there certainly have been cases
where delaying IRQ allocation has caused troubles.

I really like the idea of moving to the IRQ == GSI model for ia64.
But of course, we'll have to get rid of the 180-vector limit to
make that work, too.

Bjorn
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