Cannot detect SATA disks w/ CONFIG_SATA_PMP w/o actually using SATA multiplier

[Lin Mac]

Hi,

I found that if I enabled CONFIG_SATA_PMP while not using multiplier
and connect the disks directly to the board, the disk cannot be found
due to software reset always failed.

With arm/cns3xxx
linux-2.6.37-rc3
ahci-platform driver

# modprobe ahci-platform
[   12.790000] ahci ahci.0: forcing PORTS_IMPL to 0x3
[   12.800000] ahci ahci.0: AHCI 0001.0100 32 slots 2 ports 3 Gbps 0x3
impl platform mode
[   12.810000] ahci ahci.0: flags: ncq sntf pm led clo only pmp pio
slum part ccc
[   12.850000] scsi0 : ahci_platform
[   12.860000] scsi1 : ahci_platform
[   12.870000] ata1: SATA max UDMA/133 irq_stat 0x00400040, connection
status changed irq 65
[   12.880000] ata2: SATA max UDMA/133 mmio [mem
0x83000000-0x83ffffff] port 0x180 irq 65
[   13.240000] ata2: SATA link down (SStatus 0 SControl 300)
[   18.900000] ata1: link is slow to respond, please be patient (ready=0)
[   22.930000] ata1: softreset failed (device not ready)
[   28.940000] ata1: link is slow to respond, please be patient (ready=0)
[   32.970000] ata1: softreset failed (device not ready)
[   38.980000] ata1: link is slow to respond, please be patient (ready=0)
[   68.030000] ata1: softreset failed (device not ready)
[   68.040000] ata1: limiting SATA link speed to 1.5 Gbps
[   70.280000] ata1: SATA link down (SStatus 1 SControl 310)

With some debug, ahci_check_ready always get PORT_TFDATA(20)=0x1d0

While using multiplier with CONFIG_SATA_PMP enabled, or using disks
directly without CONFIG_SATA_PMP have no issue.
After some googling, it seems common and the only fix is to disable
CONFIG_SATA_PMP.
So, before I keep on going, I would like to know whether this is a
limitation, or a bug?

Best Regards,
Mac Lin