Re: ahci, SActive flag, and the HD activity LED

Jens Axboe
2005-08-02T16:33:53Z

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