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.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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.
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
On Mon, Mar 09, 2009 at 11:09:02AM -0700, Randy Dunlap wrote:
> >> 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.
There's every bit as much typechecking with the approach I outlined as
there was with the original.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."