linux-kernel - Re: [PATCH v4 9/9] PCI/MSI: Introduce pci_auto_enable

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Message-ID: <20131223144418.GA11342@dhcp-26-207.brq.redhat.com>
Date:	Mon, 23 Dec 2013 15:44:18 +0100
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	Michael Ellerman <michael@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tejun Heo <tj@...nel.org>,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Laight <David.Laight@...LAB.COM>,
	Mark Lord <kernel@...rt.ca>, "H. Peter Anvin" <hpa@...or.com>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v4 9/9] PCI/MSI: Introduce pci_auto_enable_msi*() family
 helpers

On Tue, Dec 17, 2013 at 05:30:02PM -0700, Bjorn Helgaas wrote:
> > +int pci_auto_enable_msi_range(struct pci_dev *dev, struct msix_entry *entries,
> > +			      int minvec, int maxvec)

[...]

> > +If this function returns a positive number it indicates at least the
> > +returned number of MSI interrupts have been successfully allocated (it may
> > +have allocated more in order to satisfy the power-of-two requirement).
> 
> I assume this means the return value may be larger than the "maxvec"
> requested, right?  And the driver is free to use all the vectors up to the
> return value, even those above maxvec, right?

No, the returned value may not be larger than the "maxvec" ever. This is just
paraphrasing the semantics of exisitng pci_enable_msi_block() interface - a
value written to MMC register might be larger than the returned value, but the
driver may not use the extra vectors it did not request.

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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