Re: Thinking about NCQ support for NetBSD

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Tue, May 21, 2013 at 11:14:03PM -0700, Brian Buhrow wrote:
>       hello.  Recently I've been working on some fixes for the mpt(4)
> driver.  In the process of getting those fixes working, I began thinking
> about how hard it would be to get NCQ tag queueing working for NetBSD.  In
> the process of getting my head around what is involved, I find I have
> questions.  If someone wants to share what they know here or privately,
> I'd be interested in reading.
> 
> 1.  I read a document that discussed ahcisata and its advantages over
> traditional IDE mode.  One of the advantages it touted was that ahcisata
> would support NCQ tag queueing.  Is it a requirement in order for NCQ
> tag queueing to work that the interface card support it as well?  For
> example, the viaide(4) driver supports SATA controllers, but says nothing
> about NCQ support or the potential for it.

Yeah, you need something with more than just wdc(4)/pciide(4)-style
registers.  ahcisata(4), siisata(4), and mvsata(4) would be capable of
NCQ.

> 2.  Does anyone have any preliminary patches for NCQ support that the never
> got into the system?

The first issue is the ata(4) layer, which doesn't currently support
multiple outstanding commands per drive.  What little work I did on it
I probably swept away, as nothing useful came of it last I tried.

        Jonathan Kollasch