Re: [virtio-dev] [PATCH] virtio-ccw: introduce revisions

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

On Tue, Oct 08, 2013 at 05:19:05PM +0200, Cornelia Huck wrote:
> Provide a new ccw that allows devices and drivers to operate on selected
> revision levels.
> 
> VIRTIO-42
> 
> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

So basically, CCW_CMD_SET_VIRTIO_REV re-implements the VIRTIO_1 feature
bit in a device specific manner.
Now that we have FEATURES_OK, this does not seem to be needed?


> ---
>  virtio-v1.0-wd01-part1-specification.txt |   77 +++++++++++++++++++++++++++---
>  1 file changed, 71 insertions(+), 6 deletions(-)
> 
> diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt
> index 4eb770e..3ba7f52 100644
> --- a/virtio-v1.0-wd01-part1-specification.txt
> +++ b/virtio-v1.0-wd01-part1-specification.txt
> @@ -1551,13 +1551,78 @@ virtio:
>  #define CCW_CMD_WRITE_CONF 0x21
>  #define CCW_CMD_WRITE_STATUS 0x31
>  #define CCW_CMD_READ_VQ_CONF 0x32
> +#define CCW_CMD_SET_VIRTIO_REV 0x83
>  
>  2.3.3.2. Device Initialization
>  ------------------------------
>  
>  virtio-ccw uses several channel commands to set up a device.
>  
> -2.3.3.2.1. Configuring a Virtqueue
> +2.3.3.2.1. Setting the Virtio Revision
> +--------------------------------------
> +
> +CCW_CMD_SET_VIRTIO_REV is issued by the driver to set the revision of
> +the virtio standard it intends to drive the device with. It uses the
> +following communication structure:
> +
> +struct virtio_rev_info {
> +       __u16 revision;
> +       __u16 length;
> +       __u8 data[];
> +};
> +
> +revision contains the desired revision id, length the length of the
> +data portion and data revision-dependent additional desired options.
> +
> +The following values are supported:
> +
> +------------------------------------------------------------------
> +| revision | length | data      | remarks                        |
> +|----------|--------|-----------|--------------------------------|
> +| 0        | 0      | <empty>   | legacy interface; transitional |
> +|          |        |           | devices only                   |
> +|----------|--------|-----------|--------------------------------|
> +| 1        | 0      | <empty>   | Virtio 1.0                     |
> +|----------|--------|-----------|--------------------------------|
> +| 2-n      |        |           | reserved for later revisions   |
> +------------------------------------------------------------------
> +
> +A device MUST post a unit check with command reject for any revision
> +it does not support. For any invalid combination of revision, length
> +and data, it MUST post a unit check with command reject as well. A
> +non-transitional device MUST reject revision id 0.
> +
> +A driver SHOULD start with trying to set the highest revision it
> +supports and continue with lower revisions if it gets a command reject.
> +
> +A driver MUST NOT issue any other virtio-ccw specific channel commands
> +prior to setting the revision.
> +
> +A device MUST answer with command reject to any virtio-ccw specific
> +channel command that is not contained in the revision selected by the
> +driver.
> +
> +After a revision has been successfully selected by the driver, it
> +MUST NOT attempt to select a different revision. A device MUST answer
> +to any such attempt with a command reject.
> +
> +2.3.3.2.1.1. Legacy Interfaces: A Note on Setting the Virtio Revision
> +---------------------------------------------------------------------
> +
> +A legacy device will not support the CCW_CMD_SET_VIRTIO_REV and answer
> +with a command reject. A non-transitional driver MUST stop trying to
> +operate this device in that case. A transitional driver MUST operate
> +the device as if it had been able to set revision 0.
> +
> +A legacy driver will not issue the CCW_CMD_SET_VIRTIO_REV prior to
> +issueing other virtio-ccw specific channel commands. A non-transitional
> +device therefore MUST answer any such attempts with a command reject.
> +A transtional device MUST assume in this case that the driver is a
> +legacy driver and continue as if the driver selected revision 0. This
> +implies that the device MUST reject any command not valid for revision
> +0, including a subsequent CCW_CMD_SET_VIRTIO_REV.
> +
> +2.3.3.2.2. Configuring a Virtqueue
>  ----------------------------------
>  
>  CCW_CMD_READ_VQ_CONF is issued by the guest to obtain information
> @@ -1586,7 +1651,7 @@ queue contains the guest address for queue index. The actual
>  number of allocated buffers is transmitted in num and their
>  alignment in align.
>  
> -100.3.3.2.1.  Virtqueue Layout
> +100.3.3.2.2.  Virtqueue Layout
>  ------------------------------
>  
>  The virtqueue is physically contiguous, with padded added to make the
> @@ -1606,14 +1671,14 @@ The calculation for total size is as follows:
>  	          + ALIGN(sizeof(u16)*3 + sizeof(struct vring_used_elem)*num);
>  	}
>  
> -2.3.3.2.2. Communicating Status Information
> +2.3.3.2.3. Communicating Status Information
>  -------------------------------------------
>  
>  The guest can change the status of a device via the
>  CCW_CMD_WRITE_STATUS command, which transmits an 8 bit status
>  value.
>  
> -2.3.3.2.3. Handling Device Features
> +2.3.3.2.4. Handling Device Features
>  -----------------------------------
>  
>  Feature bits are arranged in an array of 32 bit values, making
> @@ -1640,7 +1705,7 @@ For communicating its device features to the host, the guest may
>  use the CCW_CMD_WRITE_FEAT command, denoting a features/index
>  combination.
>  
> -2.3.3.2.4. Device Configuration
> +2.3.3.2.5. Device Configuration
>  -------------------------------
>  
>  The device's configuration space is located in host memory. It is
> @@ -1656,7 +1721,7 @@ read from.
>  
>  In both cases, the complete configuration space is transmitted.
>  
> -2.3.3.2.5. Setting Up Indicators
> +2.3.3.2.6. Setting Up Indicators
>  --------------------------------
>  
>  To communicate the location of the indicator bits for host->guest
> -- 
> 1.7.9.5
> 
> 
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