From: jbarnes@sgi.com (Jesse Barnes)

Here's the patch to add the new _relaxed variants for PIO read accesses.
It's been ack'd by gregkh and Grant Grundler, and I think it's ready to
go.

PCI ordering rules also guarantee that PIO read responses arrive after any
outstanding DMA writes on that bus, since for some devices the result of a
readb() call may signal to the driver that a DMA transaction is complete.  In
many cases, however, the driver may want to indicate that the next readb()
call has no relation to any previous DMA writes performed by the device.  The
driver can use the readb_relaxed() for these cases, although only some
platforms will honor the relaxed semantics.