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

[Jeff Garzik <jeff@garzik.org>]

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.

	Jeff