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    SubjectRe: ahci, SActive flag, and the HD activity LED
    On Tue, Aug 02 2005, Martin Wilck wrote:
    > Hello Jeff, hello Jens, hello everybody,
    >
    > I am referring to the debate about whether or not setting the SActive
    > bit for non-NCQ ATA commands (e.g. http://lkml.org/lkml/2005/5/26/142).
    >
    > In our machines, this behavior of the Linux AHCI driver causes the HD
    > activity LED to stay on all the time. If I apply the attached trivial
    > patch (this is for the RedHat EL4.0-U1 kernel), the LED behaves nicely.
    >
    > Jeff has stated in the above thread that "SActive is intentionally used
    > for non-NCQ devices". However I find clear indication in the specs that
    > the SActive flag should be set if and only if tagged queuing is being
    > used, and only for a specified subset of commands that support queuing
    > (http://www.t13.org/docs2005/D1699r1e-ATA8-ACS.pdf, secs. 4.19 and
    > 4.20). The current mainline driver doesn't use queuing.
    >
    > If I am reading the specs correctly, that'd mean the ahci driver is
    > wrong in setting the SActive bit. Could you please comment? Jeff, in
    > particular, could you please give more detail why you say this flag is
    > "intentionally used"?

    I completely agree, that was my reading of the spec as well and hence my
    original posts about this in the NCQ thread.

    --
    Jens Axboe

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