ata: libahci: clear pending interrupt status

When a CRC error occurs, the HBA asserts an interrupt to indicate an
interface fatal error (PxIS.IFS). The ISR clears PxIE and PxIS, then
does error recovery. If the adapter receives another SDB FIS
with an error (PxIS.TFES) from the device before the start of the EH
recovery process, the interrupt signaling the new SDB cannot be
serviced as PxIE was cleared already. This in turn results in the HBA
inability to issue any command during the error recovery process after
setting PxCMD.ST to 1 because PxIS.TFES is still set.

According to AHCI 1.3.1 specifications section 6.2.2, fatal errors
notified by setting PxIS.HBFS, PxIS.HBDS, PxIS.IFS or PxIS.TFES will
cause the HBA to enter the ERR:Fatal state. In this state, the HBA
shall not issue any new commands.

To avoid this situation, introduce the function
ahci_port_clear_pending_irq() to clear pending interrupts before
executing a COMRESET. This follows the AHCI 1.3.1 - section 6.2.2.2
specification.

Signed-off-by: Szuying Chen <Chloe_Chen@asmedia.com.tw>
Fixes: e0bfd149

 ("[PATCH] ahci: stop engine during hard reset")
Cc: stable@vger.kernel.org
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>