[PATCH v2 0/1] ccw: provide status accessor for driver

On Mon, 19 Oct 2015 10:31:53 +0200
Cornelia Huck <> wrote:
> ccw currently allows the driver to update the status via the
> CCW_CMD_WRITE_STATUS command; however, it does not allow the driver to
> retrieve the current status at the device, which is needed to properly
> support DEVICE_NEEDS_RESET.
>
> Therefore, provide a new command CCW_CMD_READ_STATUS allowing the driver
> to retrieve the device status. Provide this command when revision 2 has
> been negotiated.
>
> VIRTIO-117
>
> Signed-off-by: Cornelia Huck <>
> ---
>  content.tex | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)

Ping.

Was going through my backlog and noticed READ_STATUS languishing here.

Unless someone objects, I'll open the issue and target this for 1.1.

The guest kernel and qemu patches still basically apply; I'll repost
them.

>
> diff --git a/content.tex b/content.tex
> index 4be0f7d..d8bacbb 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2505,6 +2505,7 @@ virtio:
>  #define CCW_CMD_WRITE_STATUS 0x31
>  #define CCW_CMD_READ_VQ_CONF 0x32
>  #define CCW_CMD_SET_VIRTIO_REV 0x83
> +#define CCW_CMD_READ_STATUS 0x72
>  \end{lstlisting}
>
>  \devicenormative{\subsubsection}{Basic Concepts}{Virtio Transport Options / Virtio over channel I/O / Basic Concepts}
> @@ -2565,7 +2566,9 @@ The following values are supported:
>  \hline
>  1
& 0
& <empty>
& Virtio 1.0 \\
>  \hline
> -2-n
&
&
& reserved for later revisions \\
> +2
& 0
& <empty>
& CCW_CMD_READ_STATUS support \\
> +\hline
> +3-n
&
&
& reserved for later revisions \\
>  \hline
>  \end{tabular}
>
> @@ -2683,18 +2686,31 @@ As described in
>  a device sometimes fails to set the \field{status} field: For example, it
>  might fail to accept the FEATURES_OK status bit during device initialization.
>
> +With revision 2, CCW_CMD_READ_STATUS is defined: It reads an 8 bit status
> +value from the device and acts as a reverse operation to CCW_CMD_WRITE_STATUS.
> +
>  \drivernormative{\paragraph}{Communicating Status Information}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Communicating Status Information}
>
>  If the device posts a unit check with command reject in response to the
>  CCW_CMD_WRITE_STATUS command, the driver MUST assume that the device failed
>  to set the status and the \field{status} field retained its previous value.
>
> +If at least revision 2 has been negotiated, the driver SHOULD use the
> +CCW_CMD_READ_STATUS command to retrieve the \field{status} field after
> +a configuration change has been detected.
> +
> +If not at least revision 2 has been negotiated, the driver MUST NOT attempt
> +to issue the CCW_CMD_READ_STATUS command.
> +
>  \devicenormative{\paragraph}{Communicating Status Information}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Communicating Status Information}
>
>  If the device fails to set the \field{status} field to the value written by
>  the driver, the device MUST assure that the \field{status} field is left
>  unchanged and MUST post a unit check with command reject.
>
> +If at least revision 2 has been negotiated, the device MUST return the
> +current \field{status} field if the CCW_CMD_READ_STATUS command is issued.
> +
>  \subsubsection{Handling Device Features}\label{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Handling Device Features}
>
>  Feature bits are arranged in an array of 32 bit values, making