[virtio-dev] Re: [virtio-comment] Re: [PATCH 3/5] virtqueue: constraints for virtqueue state

Zhu, Lingshan
2023-09-19T07:56:27Z

On 9/19/2023 1:30 AM, Michael S. Tsirkin wrote:
> On Mon, Sep 18, 2023 at 11:02:18AM +0800, Zhu, Lingshan wrote:
>>
>> On 9/15/2023 7:16 PM, Michael S. Tsirkin wrote:
>>> On Fri, Sep 15, 2023 at 10:59:29AM +0800, Zhu, Lingshan wrote:
>>>> On 9/14/2023 7:30 PM, Michael S. Tsirkin wrote:
>>>>> On Wed, Sep 06, 2023 at 04:16:35PM +0800, Zhu Lingshan wrote:
>>>>>> This commit specifies the constraints of the virtqueue state,
>>>>>> and the actions should be taken by the device when SUSPEND
>>>>>> and DRIVER_OK is set
>>>>>>
>>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
>>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>>>>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
>>>>>> ---
>>>>>> content.tex | 19 +++++++++++++++++++
>>>>>> 1 file changed, 19 insertions(+)
>>>>>>
>>>>>> diff --git a/content.tex b/content.tex
>>>>>> index 0fab537..9d727ce 100644
>>>>>> --- a/content.tex
>>>>>> +++ b/content.tex
>>>>>> @@ -594,6 +594,25 @@ \subsection{\field{Used State} Field}
>>>>>> When VIRTIO_RING_F_PACKED is not negotiated, the 16-bit value of \field{used_idx}
>>>>>> is always 0
>>>>>> +\drivernormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated but VIRTIO_RING_F_PACKED not been negotiated,
>>>>>> +the driver SHOULD NOT access \field{Used State} of any virtqueues, it SHOULD use the
>>>>>> +used index in the used ring.
>>>>>> +
>>>>>> +\devicenormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated, the device SHOULD only accept setting
>>>>>> +Virtqueue State of any virtqueues when DRIVER_OK is not set in \field{device status},
>>>>>> +or both of DRIVER_OK and SUSPEND are set in \field{device status}.
>>>>>> +Otherwise the device MUST ignore any writes to Virtqueue State of any virtqueues.
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE have been negotiated, when SUSPEND is set,
>>>>>> +the device MUST record the Virtqueue State of every enabled virtqueue
>>>>>> +in \field{Available State} and \field{Used State} respectively,
>>>>> record how?
>>>> This is transport specific, for PCI they are recorded in the common config
>>>> space,
>>>> two new fields of them are introduced in patch 5.
>>> that is not enough space to record state for every enabled vq.
>> They can work with queue_select like many other vq configurations.
> queue select is under driver control.
queue_select works for other fields like queue_size which is also RW.

It looks no difference between queue_size and vq_state.
>
>
>> I will mention this in the comment.
>>>>>> +and correspondingly restore the Virtqueue State of every enabled virtqueue
>>>>>> +from \field{Available State} and \field{Used State} when DRIVER_OK is set.
>>>>> when is that?
>>>> When the DRIVER sets DRIVER_OK and done before the device presents
>>>> DRIVER_OK.
>>> I don't really understand the flow here. does SUSPEND clear DRIVER_OK
>>> then?
>> SUSPEND does not clear DRIVER, I think this is not a must.
> then I don't get what does "when DRIVER_OK is set" mean - it stays
> set all the time.
That means the driver sets DRIVER_OK.

I am not a native speaker, but This wording can be found throughout the
spec, e.g.:

2.1.2 Device Requirements: Device Status Field

If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET, the device MUST
send a device configuration
change notification to the driver.
>
>
>>>
>>>>>> +
>>>>>> \input{admin.tex}
>>>>>> \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
>>>>>> --
>>>>>> 2.35.3
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