[OASIS Issue Tracker] Commented: (VIRTIO-38) New status bit FEATURES_OK

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ http://tools.oasis-open.org/issues/browse/VIRTIO-38?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34735#action_34735 ] 

Michael Tsirkin commented on VIRTIO-38:
---------------------------------------

for an alternative proposal (DEVICE_OK instead of FEATURES_OK), see
https://tools.oasis-open.org/issues/browse/VIRTIO-30



> New status bit FEATURES_OK
> --------------------------
>
>                 Key: VIRTIO-38
>                 URL: http://tools.oasis-open.org/issues/browse/VIRTIO-38
>             Project: OASIS Virtual I/O Device (VIRTIO) TC
>          Issue Type: Bug
>            Reporter: Rusty Russell
>
> The current spec states :
> 2.2.1. Device Initialization
> ---------------------------
> 1. Reset the device. This is not required on initial start up.
> 2. The ACKNOWLEDGE status bit is set: we have noticed the device.
> 3. The DRIVER status bit is set: we know how to drive the device.
> 4. Device-specific setup, including reading the device feature
>   bits, discovery of virtqueues for the device, optional per-bus
>   setup, and reading and possibly writing the device's virtio
>   configuration space.
> 5. The subset of device feature bits understood by the driver is
>    written to the device.
> 6. The DRIVER_OK status bit is set.
> 7. The device can now be used (ie. buffers added to the
>    virtqueues)[4]
> But Linux doesn't do this, and in fact, can't do it easily.  Device initialization includes setting up virtqueues and even (for virtio_blk) scanning the partition table.
> Add  a new step, FEATURES_OK, which predates any use and explicitly acks the feature bits.

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