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    SubjectRe: [PATCH] Add quirk to set AHCI mode on ICH boards
    Alan Cox wrote:
    > On Thu, 8 Nov 2007 22:46:22 -0500
    > Jeff Garzik <jeff@garzik.org> wrote:
    >
    >
    >> On Thu, Nov 08, 2007 at 10:29:37PM -0500, Mark Lord wrote:
    >>
    >>> And I might even privately patch my own kernels to map the ACHI BAR
    >>> in the cases where the BIOS didn't...
    >>>
    >> The inability to do this in the general case is the main reason why
    >> AHCI was not unconditionally enabled, even in IDE mode, when it was
    >> originally added... :/
    >>
    >
    > We've done it all the time for various devices without problems (eg S3
    > video cards). I'd like to see it go in - although perhaps attached to a
    > force_ahci boot param initially
    >

    There is one problem with force enabling ahci. You'll loose the CDROM on
    Dell laptops.
    Prior to force-enabling ahci there is one "device" that sees the 2 sata
    channels, and the 2 ide channels.
    When you force-enable ahci, this device becomes the ahci controller (it
    changes the device id),
    and the IDE controller will appear as a separate new device (with
    another device id), but it is disabled.

    There are registers on the ICH7 that allows you to set enabled/disabled
    status, but according to the documentation you should not enable a
    device after it has been disabled. In practice I couldn't get the CDROM
    to get re-enabled:
    * either nothing happend
    * spurious irqs were sent that nobody handles, unless I used irq=poll;
    but still no cdrom.

    Force-enabling AHCI, and not trying to enable the CDROM works, although
    I occasionally got NCQ errors.

    For a (long) discussion see this thread on the powertop mailing list:
    http://www.bughost.org/pipermail/power/2007-June/000533.html
    http://www.bughost.org/pipermail/power/2007-June/000573.html

    And there is also another slightly different approach:
    http://mjg59.livejournal.com/76062.html

    Best regards,
    --Edwin






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