Re: [RFC][PATCH] ahci: Add support for Promise PDC42819

[Mikael Pettersson <mikpe@it.uu.se>]

Jeff Garzik writes:
 > Mark Nelson wrote:
 > > On Thu, Sep 4, 2008 at 8:37 PM, Jeff Garzik <jeff@garzik.org> wrote:
 > >> Mark Nelson wrote:
 > >>> On Tue, Sep 2, 2008 at 10:08 PM, Mikael Pettersson <mikpe@it.uu.se> wrote:
 > >>>> Mark Nelson writes:
 > >>>>  > On Tue, Sep 2, 2008 at 9:19 PM, Jeff Garzik <jeff@garzik.org> wrote:
 > >>>>  > > Mark Nelson wrote:
 > >>>>  > >>
 > >>>>  > >> Add an appropriate entry for the Promise PDC42819 controller. It
 > >>>> has an
 > >>>>  > >> AHCI mode and seems to work correctly with board_ahci.
 > >>>>  > >>
 > >>>>  > >> This chip is found on Promise's FastTrak TX2650 (2 port) and TX4650
 > >>>> (4
 > >>>>  > >> port)
 > >>>>  > >> software-based RAID cards (for which there is a binary driver,
 > >>>> t3sas) and
 > >>>>  > >> can be found on some motherboards, for example the MSI K9A2
 > >>>> Platinum,
 > >>>>  > >> which calls the chip a Promise T3 controller.
 > >>>>  > >>
 > >>>>  > >> Signed-off-by: Mark Nelson <mdnelson8@gmail.com>
 > >>>>  > >> ---
 > >>>>  > >> Apparently this chip also supports SAS disks, will these work with
 > >>>> the
 > >>>>  > >> ahci driver (I've only tested with normal desktop SATA disks)?
 > >>>>  > >
 > >>>>  > > ahci is definitely SATA-only, so I wonder how they modified AHCI to
 > >>>> support
 > >>>>  > > SAS transport...
 > >>>>  >
 > >>>>  > That is a good question. From my understanding the controller is a SAS
 > >>>>  > controller that can drive SATA disks (as I guess all SAS controllers
 > >>>> can
 > >>>>  > do...). Could it be that the controller can be setup to act as an AHCI
 > >>>>  > SATA controller or if the right registers are poked a SAS controller?
 > >>>>
 > >>>> Based on how the sata_promise-supported chips work I'd guess that they
 > >>>> have dual programming interfaces with AHCI for JBOD SATA and a native
 > >>>> one (perhaps just additional control registers) for SAS and raid.
 > >>>>
 > >>> That's interesting; and makes sense. I'm guessing that we won't end up
 > >>> with an open source driver that can do SAS on these chips then... But
 > >>> for now at least we can use them as SATA controllers and if Promise
 > >>> wants to come to the table with specs or datasheets they can in the
 > >>> future. I'm just happy to be able to use my eSATA ports (and perhaps
 > >>> the possibility of getting my hard disk off the SB600, although I should
 > >>> benchmark both controllers before jumping to any conclusions).
 > >> FWIW, I'll poke my Promise contacts, but they have gone mostly silent in the
 > >> past year, so don't get your hopes up...
 > > 
 > > Thanks Jeff!
 > > 
 > > No need for hope - we have ahci now :)
 > 
 > Well, I still think this PCI ID addition leaves open the possibility 
 > that plugging in a SAS disk could hang the system or similar misbehavior.

Agreed, there's no telling what Promise-specific magic is needed
to properly drive the T3.

/Mikael