Re: [virtio-dev] Re: [PATCH v1 2/2] virtio-mmio: add features for virtio-mmio specification version 3

[Liu, Jing2]

[...]

> > > > +
> > > > +/* RO: MSI feature enabled mask */
> > > > +#define VIRTIO_MMIO_MSI_ENABLE_MASKÂÂÂ 0x8000
> > > > +/* RO: Maximum queue size available */
> > > > +#define VIRTIO_MMIO_MSI_STATUS_QMASKÂÂÂ 0x07ff
> > > > +/* Reserved */
> > > > +#define VIRTIO_MMIO_MSI_STATUS_RESERVEDÂÂÂ 0x7800
> > > > +
> > > > +#define VIRTIO_MMIO_MSI_CMD_UPDATEÂÂÂ 0x1
> > >
> > >
> > > I believe we need a command to read the number of vectors supported 
> > > by the device, or 2048 is assumed to be a fixed size here?
> >
> > For not bringing much complexity, we proposed vector per queue and 
> > fixed relationship between events and vectors.
>
>
> It's a about the number of MSIs not the mapping between queues to 
> MSIs.And it looks to me it won't bring obvious complexity, just need a 
> register to read the #MSIs. Device implementation may stick to a fixed 
> size.

Based on that assumption, the device supports #MSIs = #queues + #config. 
Then driver need not read the register.

We're trying to make such kind of agreement on spec level.

> Having few pages for a device that only have one queue is kind of a 
> waste.

Could I ask what's the meaning of few pages here? BTW, we didn't define 
MSIx-like tables for virtio-mmio.

Thanks,

Jing

> Thanks
>
>
> > So the number of vectors supported by device is equal to the total 
> > number of vqs and config.
> >
> > We will try to explicitly highlight this point in spec for later 
> > version.
> >
> >
> > Thanks!
> >
> > Jing
> >
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