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Subject: queue_enable vs QueueReady


I found ambiguity in the virtio specification:

In PCI part, it describes the queue_enable as:

The driver uses this to selectively prevent the device from executing requests from this virtqueue. 1 - enabled; 0 - disabled.

In MMIO part, it describes the QueueReady as:

Writing one (0x1) to this register notifies the device that it can execute requests from this virtual queue. Reading from this register returns the last value written to it. Both read and write accesses apply to the queue selected by writing to QueueSel.

If I understand this correctly, they have the same meaning, but the driver requirements section looks conflict:

PCI said: The driver MUST NOT write a 0 to queue_enable.

MMIO said:

To stop using the queue the driver MUST write zero (0x0) to this QueueReady and MUST read the value back to ensure synchronization.

So we can't disable a queue via queue_enable but QueueReady. Any reason for such inconsistency?


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