Re: [Xen-devel] [PATCH v5 08/10] x86/PCI: read MSI-X table entry count early

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.08.2019 17:16, Roger Pau Monné  wrote:
> On Tue, Aug 06, 2019 at 04:47:28PM +0200, Jan Beulich wrote:
> > On 06.08.2019 16:25, Roger Pau Monné  wrote:
> > > On Tue, Aug 06, 2019 at 03:10:40PM +0200, Jan Beulich wrote:
> > > > @@ -350,6 +353,10 @@ static struct pci_dev *ºalloc_pdev(struct
> > > >                return NULL;
> > > >            }
> > > >            spin_lock_init(&msix->table_lock);
> > > > +
> > > > +        ctrl = pci_conf_read16(pdev->sbdf, msix_control_reg(pos));
> > > > +        msix->nr_entries = msix_table_size(ctrl);
> > > Since you store the number of entries here, why not also store the
> > > position of the MSI-X capability since it's also immutable?
> > >
> > > That would prevent having to fetch it again in msix_capability_init.
> > I do consider this as something worthwhile to do in the future, but
> > not here: The field to store this doesn't exist in struct arch_msix
> > (yet), and hence would likely want moving from struct msi_attrib.
> > This is beyond the scope of this patch.
> Oh I see. So the position it's actually stored in msi_attrib, and is
> used by both MSI and MSI-X, in which case what I'm proposing would be
> worse, since the field would only be used by MSI-X.
Right, if we wanted to store it, we'd want to cover both MSI and
MSI-X (and hence it would need to be a field outside of struct
arch_msix).

> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks.

Jan

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