linux-kernel - Re: [PATCH v10 3/7] PCI: reserve bus range for SR-IOV device

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Message-ID: <20090309081337.GB4638@yzhao-otc.sh.intel.com>
Date:	Mon, 9 Mar 2009 16:13:37 +0800
From:	Yu Zhao <yu.zhao@...el.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 3/7] PCI: reserve bus range for SR-IOV device

On Sat, Mar 07, 2009 at 04:20:24AM +0800, Matthew Wilcox wrote:
> On Fri, Feb 20, 2009 at 02:54:44PM +0800, Yu Zhao wrote:
> > +static inline void virtfn_bdf(struct pci_dev *dev, int id, u8 *busnr, u8 *devfn)
> > +{
> > +	u16 bdf;
> > +
> > +	bdf = (dev->bus->number << 8) + dev->devfn +
> > +	      dev->sriov->offset + dev->sriov->stride * id;
> > +	*busnr = bdf >> 8;
> > +	*devfn = bdf & 0xff;
> > +}
> 
> I find the interface here a bit clunky -- a function returning void
> while having two OUT parameters.  How about this variation on the theme
> (viewers are encouraged to come up with their own preferred
> implementations and interfaces):
> 
> static inline __pure u16 virtfn_bdf(struct pci_dev *dev, int id)
> {
> 	return (dev->bus->number << 8) + dev->devfn + dev->sriov->offset +
> 		dev->sriov->stride * id;
> }
> 
> #define VIRT_BUS(dev, id)	(virtfn_bdf(dev, id) >> 8)
> #define VIRT_DEVFN(dev, id)	(virtfn_bdf(dev, id) & 0xff)
> 
> We rely on GCC to do CSE and not actually invoke virtfn_bdf more than
> once.

Yes, that's a good idea. Will replace that function with macros.
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