without waiting for device readiness (or at least not updating FIS receive
area in time). To workaround that, special quirk was added earlier to wait
for the FIS receive area update. But it was found that under same PCI ID
0x91231b4b and revision 0x11 there are two completely different chip
versions (firmware?): HBA and RAID. The problem is that RAID version in
some cases, such as hot-plug, does not update FIS receive area at all!
To workaround that, differentiate the chip versions by their capabilities,
and, if RAID version found, skip FIS receive area update waiting and read
device signature from the PxSIG register instead. This method doesn't work
for HBA version when PMP attached, so keep using previous workaround there.
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