On Wed, 17 Jan 2018 20:02:44 +0100
KarimAllah Ahmed <karahmed@xxxxxxxxxx> wrote:
> On 01/17/2018 07:49 PM, Alex Williamson wrote:
> > On Wed, 17 Jan 2018 19:30:29 +0100
> > KarimAllah Ahmed <karahmed@xxxxxxxxx> wrote:
> >
> >> ... since INTx is not supported by-spec for virtual functions.
> > But the spec also states that VFs must implement the interrupt pin
> > register as read-only zero, so either this is redundant or it's a
> > workaround for VFs that aren't quite compliant? Thanks,
>
> The end goal for me is just to NOT do the read across the PCI bus for no
> good reason. We have devices with thousands of virtual functions and
> this read is simply not useful in this case and can be optimized as I
> did. So from a functionality point of view probably the patch does not
> add any value as you mentioned, but it is really useful as a
> micro-optimization.
Thanks for the clarification, it's helpful to understand the motivation
for a patch that otherwise seems unnecessary.
Alex
> >> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> >> Cc: linux-pci@xxxxxxxxxxxxxxx
> >> Cc: linux-kernel@xxxxxxxxxxxxxxx
> >> Signed-off-by: KarimAllah Ahmed <karahmed@xxxxxxxxx>
> >> Signed-off-by: Jan H. Schönherr <jschoenh@xxxxxxxxx>
> >> ---
> >> drivers/pci/probe.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> >> index 65099d0..61002fb 100644
> >> --- a/drivers/pci/probe.c
> >> +++ b/drivers/pci/probe.c
> >> @@ -1232,6 +1232,13 @@ static void pci_read_irq(struct pci_dev *dev)
> >> {
> >> unsigned char irq;
> >>
> >> + /* Virtual functions do not have INTx support */
> >> + if (dev->is_virtfn) {
> >> + dev->pin = 0;
> >> + dev->irq = 0;
> >> + return;
> >> + }
> >> +
> >> pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
> >> dev->pin = irq;
> >> if (irq)
> >
>
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