Re: [Xen-devel] [PATCH 10/10] vpci/sriov: add support for SR-IOV capability

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.07.18 at 12:21, <roger.pau@xxxxxxxxxx> wrote:
> On Tue, Jul 03, 2018 at 10:27:59AM +0100, Wei Liu wrote:
>> On Wed, Jun 20, 2018 at 04:42:34PM +0200, Roger Pau Monne wrote:
>> > +            sriov->num_vfs = pci_conf_read16(pdev->seg, pdev->bus,
>> > +                                             PCI_SLOT(pdev->devfn),
>> > +                                             PCI_FUNC(pdev->devfn),
>> > +                                             pos + PCI_SRIOV_NUM_VF);
>> > +
>> > +            /*
>> > +             * NB: VFE needs to be enabled before calling pci_add_device 
>> > so Xen
>> > +             * can access the config space of VFs.
>> > +             */
>> > +            pci_conf_write16(pdev->seg, pdev->bus, PCI_SLOT(pdev->devfn),
>> > +                             PCI_FUNC(pdev->devfn), reg,
>> > +                             control | PCI_SRIOV_CTRL_VFE);
>> > +
>> > +            /*
>> > +             * The spec states that the software must wait at least 100ms
>> > +             * before attempting to access VF registers when enabling 
>> > virtual
>> > +             * functions on the PF.
>> > +             */
>> > +            mdelay(100);
>> 
>> IMHO delaying 100ms like this in an active system is far too long. It
>> would be better to put this into a loop and process softirqs in between
>> delays.
> 
> Ack, do you think 10ms delays would be OK?

I haven't checked yet where we are here - generally such delays would
better be implemented by pausing the caller and resuming it once the
necessary time has passed. While in Dom0 context it might be acceptable
to do what Wei and you suggest, that'll be yet one more thing to deal
with once we want to re-use the code for DomU-s.

Jan



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