Re: [PATCH v6 4/5] Add admin_queue_index register to PCI common configuration structure

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 8/1/2022 12:03 AM, Michael S. Tsirkin wrote:
> On Sun, Jul 31, 2022 at 06:43:53PM +0300, Max Gurtovoy wrote:
> > This new register will be used for querying the index of the admin
> > virtqueue of a virtio device. To configure, reset or enable the admin
> > virtqueue, the driver should follow existing queue configuration/setup
> > sequence.
> >
> > Reviewed-by: Parav Pandit <parav@nvidia.com>
> > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>
> Can you please at least add text to MMIO and CCW that drivers and
> devices must not negotiate the new feature bit? Will help avoid confusion.

why this is needed ? who will create a device and expose bits that it 
doesn't know how to implement.

And if I'll add it, we might forget to remove it later on.

> > ---
> >   content.tex | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index c15423e..5fda1a0 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -904,6 +904,9 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> >           le64 queue_device;              /* read-write */
> >           le16 queue_notify_data;         /* read-only for driver */
> >           le16 queue_reset;               /* read-write */
> > +
> > +        /* About admin virtqueue. */
> > +        le16 admin_queue_index;         /* read-only for driver */
> >   };
> >   \end{lstlisting}
> >   
> > @@ -989,6 +992,10 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> >           This field exists only if VIRTIO_F_RING_RESET has been
> >           negotiated. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> >   
> > +\item[\field{admin_queue_index}]
> > +        The device uses this to report the index of the admin virtqueue.
> > +        This field always exists. Its value is valid only if VIRTIO_F_ADMIN_VQ has been negotiated.
> > +
> >   \end{description}
> >   
> >   \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
> we have a mess with this exists versus valid. I think exists is the same

the bigest mess that we have is for things like ring_reset that are 
optionally exist according to bit negotiation.

about valid - the driver shouldn't even look on registers that it didn't 
negotiated it's feature bits. There is no reason to do so.

So yes, there is a mess but not in our proposal.

> is valid personally. Do others object if we say same as for reset here?
> Not a big deal either way, we need to clean this up later.
>
> > @@ -1075,6 +1082,9 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> >   were used before the queue reset.
> >   (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> >   
> > +For configuring the admin virtqueue, the driver MUST use the value of \field{admin_queue_index}.
> > +For more details on virtqueue configuration see section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtqueue Configuration}.
> > +
> >   \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
> >   
> >   The notification location is found using the VIRTIO_PCI_CAP_NOTIFY_CFG
> > --
> > 2.21.0