arm: a37xx: pci: Fix processing PIO transfers

arm: a37xx: pci: Fix processing PIO transfers

Trying to clear PIO_START register when it is non-zero (which indicates
that previous PIO transfer has not finished yet) causes an External
Abort with SError 0xbf000002.

This bug is currently worked around in TF-A by handling External Aborts
in EL3 and ignoring this particular SError.

This workaround was also discussed at:
https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/commit/?id=3c7dcdac5c50
https://lore.kernel.org/linux-pci/20190316161243.29517-1-repk@triplefau.lt/
https://lore.kernel.org/linux-pci/971be151d24312cc533989a64bd454b4@www.loen.fr/
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/1541

Implement a proper fix to prevent this External Abort. As it is not
possible to cancel a pending PIO transfer, simply do not start a new one
if previous has not finished yet. In this case return an error to the
caller.

In most cases this SError happens when there is no PCIe card connected
or when PCIe link is down. The reason is that in these cases a PIO
transfer takes about 1.44 seconds. For this reason we also increase the
wait timeout in pcie_advk_wait_pio() to 1.5 seconds.

If PIO read transfer for PCI_VENDOR_ID register times out, or if it
isn't possible to read it yet because previous transfer is not finished,
return Completion Retry Status value instead of failing, to give the
caller a chance to send a new read request.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>