Re: [virtio-dev] Re: [PATCH 1/2] transport-pci: Improve config msix vector description

Michael S. Tsirkin
2023-04-19T11:27:14Z

On Wed, Apr 19, 2023 at 04:25:13PM +0800, Zhu, Lingshan wrote:
>
>
> On 4/19/2023 3:05 PM, Michael S. Tsirkin wrote:
> > On Tue, Apr 11, 2023 at 10:42:19PM +0300, Parav Pandit wrote:
> > > config_msix_vector is the register that holds the MSI-X vector number
> > > for receiving configuration change related interrupts.
> > >
> > > It is not "for MSI-X".
> > >
> > > Hence, replace the confusing text with appropriate one.
> > >
> > > Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > Signed-off-by: Parav Pandit <parav@nvidia.com>
> > >
> > > ---
> > > changelog:
> > > v0->v1:
> > > - added 'here'
> > > - dropped 'receiving'
> > > ---
> > > transport-pci.tex | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/transport-pci.tex b/transport-pci.tex
> > > index 42be072..cb9fadd 100644
> > > --- a/transport-pci.tex
> > > +++ b/transport-pci.tex
> > > @@ -343,7 +343,8 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> > > Driver Feature Bits selected by \field{driver_feature_select}.
> > > \item[\field{config_msix_vector}]
> > > - The driver sets the Configuration Vector for MSI-X.
> > > + The driver writes an MSI-X vector number here for Configuration change
> > > + interrupts.
> > Hmm I think it's "the vector", not an. And the order of words
> > is unusual. We also don't normally use "writes here". Would
> >
> > Used by the driver to set the MSI-X vector number for Configuration change interrupts.
> >
> > be equally acceptable?
> Is it better also explain what is a MSI-X vector number here? Like saying
> the offset in the table or the slot number?
>
> Thanks,
> Zhu Lingshan

It does, in fact, refer to the MSI-X entry. Vector is in fact the
contents of the entry. The mixup between vector and entry dates back to
PCI spec which has text like
While more accurately termed “per-entry masking”, masking an MSI-X Table entry is still
referred to as “vector masking” so similar descriptions can be used for both MSI and MSI-
X.

> >
> >
> > > \item[\field{num_queues}]
> > > The device specifies the maximum number of virtqueues supported here.
> > > --
> > > 2.26.2
> >
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