Marvell 88SE6121 is a ahci controller, but I can't make it work with the achi 
driver.
This part:

+       else if (pdev->device == 0x6121) {
+               mmio_base = pci_iomap(pdev, 5, 0);
+               if (mmio_base == NULL) {
+                       return -ENOMEM;
+               }
+               /* turn on legacy mode */
+               writel(0, mmio_base + 0x04);
+               (void) readl(mmio_base + 0x04); /* flush */
+       }

put the ahci in legacy mode and work with pata_marvell.
Perhaps someone else can make it work whith the ahci driver.

Jose Alberto
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I forgot the Signed-off-by:

Signed-off-by: Jose Alberto Reguero <jareguero@telefonica.net>

Jose Alberto
-

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[snip]

Works-for-me: Jay Cliburn <jacliburn@bellsouth.net>

The following dmesg snippet after applying the patch shows life from the 
hitherto unsupported device:  (I connected an unpartitioned SATA HDD to it.)
==============
[   39.789326] PCI: Setting latency timer of device 0000:06:00.0 to 64
[   39.789436] ata3: PATA max UDMA/100 cmd 0xEC00 ctl 0xE882 bmdma 
0xE400 irq 28
[   39.789541] ata4: PATA max UDMA/133 cmd 0xE800 ctl 0xE482 bmdma 
0xE408 irq 28
[   39.789559] scsi2 : pata_marvell
[   39.790121] BAR5:00:02 01:7F 02:22 03:CA 04:00 05:00 06:00 07:00 
08:00 09:00 0A:00 0B:00 0C:07 0D:00 0E:00 0F:00
[   39.790152] ata3: port disabled. ignoring.
[   39.790154] ata3: reset failed, giving up
[   39.790161] scsi3 : pata_marvell
[   39.790589] BAR5:00:02 01:7F 02:22 03:CA 04:00 05:00 06:00 07:00 
08:00 09:00 0A:00 0B:00 0C:07 0D:00 0E:00 0F:00
[   39.958055] ATA: abnormal status 0x7F on port 0xE807
[   39.968869] ATA: abnormal status 0x7F on port 0xE807
[   39.979450] ata4.00: ATA-7, max UDMA/133, 488397168 sectors: LBA48
[   39.979453] ata4.00: ata4: dev 0 multi count 16
[   39.987443] ata4.00: configured for UDMA/133
[   39.987628] scsi 3:0:0:0: Direct-Access     ATA      WDC WD2500KS-00M 
02.0 PQ: 0 ANSI: 5
[   39.988524] SCSI device sdb: 488397168 512-byte hdwr sectors (250059 MB)
[   39.988546] sdb: Write Protect is off
[   39.988548] sdb: Mode Sense: 00 3a 00 00
[   39.988583] SCSI device sdb: write cache: enabled, read cache: 
enabled, doesn't support DPO or FUA
[   39.988695] SCSI device sdb: 488397168 512-byte hdwr sectors (250059 MB)
[   39.988713] sdb: Write Protect is off
[   39.988715] sdb: Mode Sense: 00 3a 00 00
[   39.988749] SCSI device sdb: write cache: enabled, read cache: 
enabled, doesn't support DPO or FUA
[   39.988781]  sdb: unknown partition table
[   39.994867] sd 3:0:0:0: Attached scsi disk sdb
[   39.994990] sd 3:0:0:0: Attached scsi generic sg1 type 0


This is the relevant portion of lspci:
==============
06:00.0 SATA controller: ...
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