[virtio-dev] Re: [PATCH] virtio: introduce SUSPEND bit in device status

On 2/18/2024 10:11 PM, Michael S. Tsirkin wrote:
> On Sun, Feb 18, 2024 at 09:23:06PM +0800, Zhu Lingshan wrote:
>> This commit allows the driver to suspend the device by
>> introducing a new status bit SUSPEND in device_status.
>>
>> This commit also introduce a new feature bit VIRTIO_F_SUSPEND
>> which indicating whether the device support SUSPEND.
>>
>> This SUSPEND bit is transport-independent.
>>
>> Signed-off-by: Zhu Lingshan <[email protected]>
>> Signed-off-by: Jason Wang <[email protected]>
>> Signed-off-by: Eugenio Pérez <[email protected]>
>
>
> Could we get some kind of dscription how this has taken into
> consideration the proposal from David Stevens?
sure thing, we can work with David together for a solution.
>
> I find it really tiring when there are competing patches with authors
> ignoring each other's work and leaving it up to reviewers to
> figure out how do the patches compare.
>
>> ---
>>   content.tex | 34 ++++++++++++++++++++++++++++++++--
>>   1 file changed, 32 insertions(+), 2 deletions(-)
>>
>> diff --git a/content.tex b/content.tex
>> index 0a62dce..3d656b5 100644
>> --- a/content.tex
>> +++ b/content.tex
>> @@ -49,6 +49,9 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
>>   
>>   \item[DEVICE_NEEDS_RESET (64)] Indicates that the device has experienced
>>     an error from which it can't recover.
>> +
>> +\item[SUSPEND (16)] When VIRTIO_F_SUSPEND is negotiated, indicates that the
>> +  device has been suspended by the driver.
>>   \end{description}
>>   
>>   The \field{device status} field starts out as 0, and is reinitialized to 0 by
>> @@ -73,6 +76,10 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
>>   recover by issuing a reset.
>>   \end{note}
>>   
>> +The driver SHOULD NOT set SUSPEND if FEATURES_OK is not set.
>> +
>> +When setting SUSPEND, the driver MUST re-read \field{device status} to ensure the SUSPEND bit is set.
>> +
>>   \devicenormative{\subsection}{Device Status Field}{Basic Facilities of a Virtio Device / Device Status Field}
>>   
>>   The device MUST NOT consume buffers or send any used buffer
>> @@ -82,6 +89,25 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
>>   that a reset is needed.  If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET, the device
>>   MUST send a device configuration change notification to the driver.
>>   
>> +The device MUST ignore SUSPEND if FEATURES_OK is not set.
>> +
>> +The device MUST ignore SUSPEND if VIRTIO_F_SUSPEND is not negotiated.
>> +
>> +The device SHOULD allow settings to \field{device status} even when SUSPEND is set.
>> +
>> +If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device SHOULD clear SUSPEND
>> +and resumes operation upon DRIVER_OK.
>> +
>> +If VIRTIO_F_SUSPEND is negotiated, when the driver sets SUSPEND,
>> +the device SHOULD perform the following actions before presenting SUSPEND bit in the \field{device status}:
>> +
>> +\begin{itemize}
>> +\item Stop consuming buffers of any virtqueues and mark all finished descriptors as used.
>> +\item Wait until all descriptors that being processed to finish and mark them as used.
>> +\item Flush all used buffer and send used buffer notifications to the driver.
>> +\item Pause its operation except \field{device status} and preserve configurations in its Device Configuration Space, see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space}
>> +\end{itemize}
>> +
>>   \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits}
>>   
>>   Each virtio device offers all the features it understands.  During
>> @@ -99,10 +125,10 @@ \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature B
>>   \begin{description}
>>   \item[0 to 23, and 50 to 127] Feature bits for the specific device type
>>   
>> -\item[24 to 41] Feature bits reserved for extensions to the queue and
>> +\item[24 to 42] Feature bits reserved for extensions to the queue and
>>     feature negotiation mechanisms
>>   
>> -\item[42 to 49, and 128 and above] Feature bits reserved for future extensions.
>> +\item[43 to 49, and 128 and above] Feature bits reserved for future extensions.
>>   \end{description}
>>   
>>   \begin{note}
>> @@ -872,6 +898,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>>   	\ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
>>   	handling features reserved for future use.
>>   
>> +  \item[VIRTIO_F_SUSPEND(42)] This feature indicates that the driver can
>> +   SUSPEND the device.
>> +   See \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}.
>> +
>>   \end{description}
>>   
>>   \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
>> -- 
>> 2.35.3


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