Re: [virtio-dev] [PATCH 3/4] vhost-user: add requirements for the notification capability

[Stefan Hajnoczi <stefanha@redhat.com>]

On Tue, Apr 23, 2019 at 06:18:18PM +0300, Nikos Dragazis wrote:
> The configuration structure for the notification capability has certain
> device/driver requirements, similar to those of the MSI-X vector
> configuration. Add these requirements to the device spec.
> 
> Signed-off-by: Nikos Dragazis <ndragazis@arrikto.com>
> ---
>  virtio-vhost-user.tex | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/virtio-vhost-user.tex b/virtio-vhost-user.tex
> index 0bfc48d..605272f 100644
> --- a/virtio-vhost-user.tex
> +++ b/virtio-vhost-user.tex
> @@ -275,6 +275,46 @@ \subsubsection{Notification structure layout}\label{sec:Device Types / Vhost-use
>  \field{VIRTIO_MSI_NO_VECTOR} to \field{notification_msix_vector} to change the
>  MSI-X vector for that notification.
>  
> +\devicenormative{\paragraph}{Notification capability}{Device Types / Vhost-user Device Backend / Additional Device Resources over PCI / Notification capability}
> +
> +If MSI-X is available, device MUST support mapping any master queue
> +event to any valid vector 0 to MSI-X \field{Table Size}. The valid

Do you mean Table Size - 1 since vector numbering is zero-based?

> +vectors are reported in \field{Table Size} in the MSI-X Capability as
> +specified in \hyperref[intro:PCI]{[PCI]}.
> +
> +Device MUST support unmapping any master queue event.
> +
> +The device MUST return vector mapped to a given master queue event,
> +(\field{NO_VECTOR} if unmapped) on read of
> +\field{notification_msix_vector}. The device MUST have all master queue
> +events unmapped upon reset.
> +
> +Devices SHOULD NOT cause mapping an event to vector to fail unless it is
> +impossible for the device to satisfy the mapping request. Devices MUST
> +report mapping failures by returning the \field{NO_VECTOR} value when
> +the relevant \field{notification_msix_vector} field is read.
> +
> +\drivernormative{\paragraph}{Notification capability}{Device Types /
> +Vhost-user Device Backend / Additional Device Resources over PCI /
> +Noification capability}
> +
> +Driver MUST support device with any MSI-X Table Size 0 to 0x7FF. Driver
> +MAY fall back on using INT\#x interrupts for a device which only
> +supports one MSI-X vector (MSI-X Table Size = 0).
> +
> +Driver MAY intepret the \field{Table Size} as a hint from the device for
> +the suggested number of MSI-X vectors to use.
> +
> +Driver MUST NOT attempt to map an event to a vector outside the MSI-X
> +Table supported by the device, as reported by \field{Table Size} in the
> +MSI-X Capability.
> +
> +After mapping an event to vector, the driver MUST verify success by
> +reading the Vector field value: on success, the previously written value
> +is returned, and on failure, \field{NO_VECTOR} is returned. If a mapping
> +failure is detected, the driver MAY retry mapping with fewer vectors,
> +disable MSI-X or report device failure.
> +
>  \subsubsection{Shared memory capability}\label{sec:Device Types / Vhost-user Device Backend / Additional Device Resources over PCI / Shared Memory capability}
>  
>  The shared memory location is found using the VIRTIO_PCI_CAP_SHARED_MEMORY_CFG
> -- 
> 2.7.4
> 
> 
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