OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.

 


Help: OASIS Mailing Lists Help | MarkMail Help

virtio-dev message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]


Subject: Re: [virtio-dev] Re: [PATCH v2] content: document SR-IOV driver requirements


On Fri, Jun 08, 2018 at 02:38:57PM +0200, Cornelia Huck wrote:
> On Fri, 8 Jun 2018 19:14:49 +0800
> Tiwei Bie <tiwei.bie@intel.com> wrote:
> 
> > On Fri, Jun 08, 2018 at 11:12:31AM +0200, Cornelia Huck wrote:
> > > On Fri,  8 Jun 2018 10:07:01 +0800
> > > Tiwei Bie <tiwei.bie@intel.com> wrote:
> > >   
> > > > Document the driver requirements for the VIRTIO_F_SR_IOV
> > > > feature bit.
> > > > 
> > > > Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> > > > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> > > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/13
> > > > ---
> > > > v2:
> > > > - Fix the commit message (MST);
> > > > - Improve the wording (MST);
> > > > - Drop unnecessary parts (MST);
> > > > 
> > > >  content.tex | 15 +++++++++++++++
> > > >  1 file changed, 15 insertions(+)
> > > > 
> > > > diff --git a/content.tex b/content.tex
> > > > index be18234..f996fad 100644
> > > > --- a/content.tex
> > > > +++ b/content.tex
> > > > @@ -5387,6 +5387,21 @@ A driver SHOULD accept VIRTIO_F_IO_BARRIER if it is offered.
> > > >  If VIRTIO_F_IO_BARRIER has been negotiated, a driver MUST use
> > > >  the barriers suitable for hardware devices.
> > > >  
> > > > +If VIRTIO_F_SR_IOV has been negotiated, a driver MAY enable
> > > > +virtual functions through the device's PCI SR-IOV capability
> > > > +structure.  A driver MUST NOT negotiate VIRTIO_F_SR_IOV if
> > > > +the device does not have a PCI SR-IOV capability structure
> > > > +or is not a PCI device.  A driver MUST negotiate  
> > > 
> > > Maybe I'm missing something obvious, but why should the device offer
> > > the feature in the first place if it does not support the functionality?  
> > 
> > The device is not allowed to offer the feature if it
> > doesn't support the functionality.
> > 
> > From my understanding, Michael suggested this to make
> > sure that in the future, the existing drivers won't
> > accept this feature bit when the VF or other transport
> > devices offer this feature bit, because some changes
> > may be necessary for drivers to really support this
> > feature offered by those devices.
> 
> So, this is supposed to be a safety net? Ok.

Yeah!

> 
> > 
> > >   
> > > > +VIRTIO_F_SR_IOV and complete the feature negotiation
> > > > +(including checking the FEATURES_OK \field{status} bit)
> > > > +before enabling virtual functions through the device's
> > > > +PCI SR-IOV capability structure.  After once successfully
> > > > +negotiating VIRTIO_F_SR_IOV, the driver MAY enable virtual
> > > > +functions through the device's PCI SR-IOV capability
> > > > +structure even if the device or the system has been fully
> > > > +or partially reset, and even without re-negotiating
> > > > +VIRTIO_F_SR_IOV after the reset.  
> > > 
> > > So, what is the general lifetime of this feature supposed to be? As
> > > written here, the driver needs to negotiate the feature once and then
> > > may enable virtual functions at any time in all eternity. Is this
> > > intended to accommodate hardware implementations, where some kind of
> > > switch is flipped once and then the functionality is available?
> > > 
> > > Also, as the device will need to negotiate the feature at least once,
> > > what is stopping it from negotiating it again in the future? Is this
> > > wording intended to allow the driver to simply use virtual functions on
> > > resume etc. prior to feature negotiation?  
> > 
> > This isn't intended to accommodate hardware implementations.
> > 
> > Yes, this is intended to allow the driver to simply use virtual
> > functions on resume etc. prior to feature negotiation.
> > 
> > > 
> > > It might be helpful to add some explanatory text outside of the
> > > conformance statement so we don't stumble over this in the future.  
> > 
> > Do you have any more specific suggestions about this?
> 
> Sorry, not really. Maybe see the other branch of this discussion?

Sure! Thanks! :)

Best regards,
Tiwei Bie

> 
> > It would be quite helpful! Thanks a lot!
> > 
> > Best regards,
> > Tiwei Bie
> > 
> > >   
> > > > +
> > > >  \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> > > >  
> > > >  A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further  
> > >   


[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]