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



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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