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