I got my Promise card and everything is up and running without problems,
using kernel 2.6.24-rc6 and the sata_promise driver out of the box:
00:0c.0 Mass storage controller: Promise Technology, Inc. PDC40775 (SATA 300 TX2plus) (rev 02)
Subsystem: Promise Technology, Inc. PDC40775 (SATA 300 TX2plus)
Flags: bus master, 66MHz, medium devsel, latency 72, IRQ 17
I/O ports at b400 [size=128]
I/O ports at b800 [size=256]
Memory at ef025000 (32-bit, non-prefetchable) [size=4K]
Memory at ef000000 (32-bit, non-prefetchable) [size=128K]
[virtual] Expansion ROM at 98020000 [disabled] [size=32K]
Capabilities: [60] Power Management version 2
Kernel driver in use: sata_promise
Drive is a Samsung HD321KJ 320 GB and hdparm says the drive does ~75
MB/s; with dd it does buffered writes at ~85 MB/s and reads ~295 MB/s. So
all in all I'd say it's not the card or the driver..
hth,
Holger