"ahci: drop intx manipulation on msi enable" breaks ULI M1575

[Timur Tabi <timur@freescale.com>]

Tejun,

Your patch

> ahci: drop intx manipulation on msi enable
>     
>     There's no need to turn off intx explicitly on msi enable.  This is
>     automatically handled by pci.  Drop it.
>     
>     This might be needed on machines if the BIOS turns intx off during
>     boot.  However, there's no evidence of such behavior for ahci and
>     the only such case seems to be ICH5 PATA according to ata_piix.
>     Also, given the way ahci operates, it's highly unlikely BIOS ever
>     disables IRQ for the controller.  However, as this change has slight
>     possibility of introducing failure, please schedule it for #upstream.

breaks SATA support on a Freescale MPC8610 HPCD (PowerPC) reference
board.  When I apply the patch, I get this result during boot:

ata1: SATA max UDMA/133 irq_stat 0x00400040, connection status changed
irq 19
ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
ata1.00: qc timeout (cmd 0xec)
ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4)
ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
ata1.00: qc timeout (cmd 0xec)
ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4)
ata1: limiting SATA link speed to 1.5 Gbps
ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
ata1.00: qc timeout (cmd 0xec)
ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4)
ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)

This board uses a ULI M1575 for SATA support.

Unfortunately, I don't know enough about SATA or PCI interrupts to
understand why you made the change or why it breaks on my board.

-- 
Timur Tabi
Linux kernel developer at Freescale