Re: [Xen-devel] [PATCH] pci: constify domain parameter of pci_get_pdev_by_domain

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Sep 08, 2017 at 03:15:40PM +0100, Andrew Cooper wrote:
> On 08/09/17 14:34, Roger Pau Monne wrote:
> > While there fix the indentation.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Cc: Tim Deegan <tim@xxxxxxx>
> > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > ---
> >  xen/drivers/passthrough/pci.c | 4 ++--
> >  xen/include/xen/pci.h         | 4 ++--
> >  2 files changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
> > index 74829e5748..469dfc6c3d 100644
> > --- a/xen/drivers/passthrough/pci.c
> > +++ b/xen/drivers/passthrough/pci.c
> > @@ -532,8 +532,8 @@ struct pci_dev *pci_get_real_pdev(int seg, int bus, int 
> > devfn)
> >      return pdev;
> >  }
> >  
> > -struct pci_dev *pci_get_pdev_by_domain(
> > -    struct domain *d, int seg, int bus, int devfn)
> > +struct pci_dev *pci_get_pdev_by_domain(const struct domain *d, int seg,
> > +                                       int bus, int devfn)
> 
> I know this isn't strictly related to the patch, but having 3 register
> parameters (and load of places elsewhere) here is extremely wasteful for
> register scheduling.  Could we introduce:
> 
> typedef union {
>     uint32_t sbdf;
>     struct {
>         uint16_t  f : 3,  /* Function */
>                   d : 5,  /* Device   */
>                   b : 8;  /* Bus      */
>         uint16_t s; /* Segment  */
>     };
> } pci_sbdf_t;
> 
> and try to start using it?

This is going to be kind of awkward to use with extended
functions...

It's not like what we have now (devfn) is much better, but if we
switch to something else I would like to be able to get the correct
function value for both normal and extended function devices from the
same field.

Roger.

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