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| -rw-r--r-- | content.tex | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/content.tex b/content.tex index 4b45678..c362a5c 100644 --- a/content.tex +++ b/content.tex @@ -2513,6 +2513,7 @@ 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} @@ -2573,7 +2574,9 @@ 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} @@ -2691,18 +2694,31 @@ 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 |