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

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Message-ID: <49B55B3E.3090502@oracle.com>
Date:	Mon, 09 Mar 2009 11:09:02 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Yu Zhao <yu.zhao@...el.com>
CC:	Matthew Wilcox <matthew@....cx>,
	"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

Yu Zhao wrote:
> 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.

That's the opposite of most changes lately.  I.e., functions (with
typechecking) are preferred.

-- 
~Randy
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