Re: [virtio-dev] [PATCH v7 2/3] virtio: pci support virtqueue reset

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

On Mon, Nov 08, 2021 at 02:22:42PM +0800, Xuan Zhuo wrote:
> PCI support virtqueue reset.
> 
> virtio_pci_common_cfg add "queue_reset" to support virtqueue reset.
> The driver uses this to selectively reset the queue.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>  content.tex | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/content.tex b/content.tex
> index fb373a5..219ad2f 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -901,6 +901,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>          le64 queue_driver;              /* read-write */
>          le64 queue_device;              /* read-write */
>          le16 queue_notify_data;         /* read-only for driver */
> +        le16 queue_reset;               /* read-write */
>  };
>  \end{lstlisting}
>  
> @@ -980,6 +981,12 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>          may benefit from providing another value, for example an internal virtqueue
>          identifier, or an internal offset related to the virtqueue number.
>          \end{note}
> +
> +\item[\field{queue_reset}]
> +        The driver uses this to selectively reset the queue.
> +        This field exists only if VIRTIO_F_RING_RESET has been
> +        negotiated. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> +
>  \end{description}
>  
>  \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
> @@ -1021,6 +1028,22 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>  
>  The device MUST present a 0 in \field{queue_enable} on reset.
>  
> +If VIRTIO_F_RING_RESET has been negotiated, the device MUST present a 0 in
> +\field{queue_enable} after the driver has reset the virtqueue via
> +\field{queue_reset}.
> +
> +If VIRTIO_F_RING_RESET has been negotiated, the device MUST present a 0 in
> +\field{queue_reset} on reset.
> +
> +If VIRTIO_F_RING_RESET has been negotiated, the device MUST present a 0 in
> +\field{queue_reset} after the virtqueue is enabled with \field{queue_enable}.
> +
> +The device MUST reset the queue when 1 is written to \field{queue_reset}, and
> +present a 1 in \field{queue_reset} after the queue has been reset, until the
> +driver re-enables the queue via \field{queue_enable} or the device is reset.
> +The device MUST present consistent default values after queue reset.
> +(see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> +
>  The device MUST present a 0 in \field{queue_size} if the virtqueue
>  corresponding to the current \field{queue_select} is unavailable.
>  
> @@ -1045,6 +1068,15 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>  
>  The driver MUST NOT write a 0 to \field{queue_enable}.
>  
> +If VIRTIO_F_RING_RESET has been negotiated, after the driver writes 1 to
> +\field{queue_reset} to reset the queue, it MUST verify that the queue
> +has been reset by reading back \field{queue_reset} and ensuring that it
> +is 1. The driver MAY re-enable the queue by writing a 1 to
> +\field{queue_enable} after ensuring that the other virtqueue fields have
> +been set up correctly. The driver MAY set driver-writeable queue configuration
> +values to different values than those that were used before the queue reset.
> +(see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> +


When does the field get a value distinct from 1? If never how does
driver know reset has completed?


>  \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
> -- 
> 2.31.0
> 
> 
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