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[Xen-devel] VT-d flush timeout

Hi all

This is continuing with previous discussion about VT-d spin loop. According 
previous discussion, we will deal with current 1 second flush timeout firstly.

After reviewing Linux IOMMU code, it uses the timeout mechanism widely, e.g., 
flush iotlb and context via register based mechanism,
    /* Make sure hardware complete it */
       dmar_readq, (!(val & DMA_CCMD_ICC)), val);

The only place it doesn't use this timeout mechanism is queue based 
invalidation. I think the reason is that the max number of queue entry is 2^15 
and we don't know how much time is needed really to flush 2^15 entries. So it 
is better to not use timeout here. Likewise, for Xen side, we will only remove 
the timeout in qi flush function and use spin for instead. 

Any comments?

best regards

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