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

[Jens Axboe <axboe@suse.de>]

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