Re: [virtio-dev] [PATCH] content: document the behaviours for SR-IOV

["Michael S. Tsirkin" <mst@redhat.com>]

Subject should be "document SR-IOV driver requirements" I think.

On Thu, Jun 07, 2018 at 09:50:50AM +0800, Tiwei Bie wrote:
> Document the device and driver behaviours for SR-IOV.
> 
> 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
> ---
>  content.tex | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/content.tex b/content.tex
> index 73981b7..3b45a6c 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -5387,6 +5387,18 @@ 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 can enable

can -> MAY

> +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
> +VIRTIO_F_SR_IOV and complete the feature negotiation
> +(including checking the FEATURES_OK \field{status} bit)

OK.

> before
> +the first time to enable virtual functions

before enabling virtual functions

> through the device's
> +PCI SR-IOV capability structure,

I'd end the sentence here and start a new one.

> and the driver MAY remember
> +the VIRTIO_F_SR_IOV feature bit negotiation result until it
> +unbinds from the device.
> +

I'm not sure what does this mean. We generally take it to mean
the DRIVER status bit and that gets cleared by device reset.

How about:

	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.


>  \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
>  
>  A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
> @@ -5403,6 +5415,10 @@ buffers in the same order in which they have been available.
>  A device MAY fail to operate further if VIRTIO_F_IO_BARRIER
>  is not accepted.
>  
> +A device SHOULD offer VIRTIO_F_SR_IOV if it is a PCI device
> +and presents a PCI SR-IOV capability structure, otherwise
> +it MUST NOT offer VIRTIO_F_SR_IOV.
> +
>  \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits}
>  
>  Transitional devices MAY offer the following:

This part has been committed aleady.

I suspect we want to add somewhere in the general section:


	If device has successfully negotiated a set of features at least once
	(by setting the FEATURES_OK \field{status} bit) then it SHOULD NOT
	fail re-negotiation of the same set of features after a device
	or system reset. Failure to do so would interfere with resume
	from suspend and error recovery.

That's a general statement though, I think it's worth a
separate issue in github.

> -- 
> 2.17.0
> 
> 
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