Reg. SATA II NCQ

Reg. SATA II NCQ

[Jaychander T]

Hi

I understand from the SATA II NCQ specs that for NCQ commands(FPDMA)
we need not have to setup the DMA (PRD) for the commands issued but
has to do
so only on reception of DMA setup FIS from the drive(throught ISR).
But in libata/ ata_qc_issue does qc prep and issue irrespective of the
protocol.

Even i glanced thro' the sil24 driver and seems to be the same.

Can someone please guide/ resolve this doubt.

Regards
Jaychander

Re: Reg. SATA II NCQ

[Tejun Heo]

Jaychander T wrote:
> I understand from the SATA II NCQ specs that for NCQ commands(FPDMA)
> we need not have to setup the DMA (PRD) for the commands issued but
> has to do

That's different thing.  NCQ protocol doesn't require DMA SETUP FIS 
which is required for normal DMA commands but the controller still needs 
to be prepped with DMA table to know from/to where transfer data.

> so only on reception of DMA setup FIS from the drive(throught ISR).
> But in libata/ ata_qc_issue does qc prep and issue irrespective of the
> protocol.

Yeap, DMA table needs to be prepped whether NCQ is used or not.

> Even i glanced thro' the sil24 driver and seems to be the same.

The same for sil24.

-- 
tejun

Re: Reg. SATA II NCQ

[Jaychander T]

Hi

Further to the discussion, can you clarify the following is correct:

Sequence for Legacy DMA:
1. Prepare SG/PRD table (qc_prep)
2. Issue command, BMDMA setup and start (Starts DMA transfer) (qc_issue)
|Issue command|Start DMA| ISR command completion.

Sequence for FPDMA:
1. Prepare SG/ PRD table (qc_prep)
2. Issue commands (but dont start DMA)
3. On reception of DMA setup FIS start DMA according to tag value.
|Issue command| Issue command| Issue command|.... ISR(DMA setup FIS) |
Start DMA | ISR | Start DMA ...

Regards
Jaychander

On 1/22/07, Tejun Heo <htejun@gmail.com> wrote:
> Jaychander T wrote:
> > I understand from the SATA II NCQ specs that for NCQ commands(FPDMA)
> > we need not have to setup the DMA (PRD) for the commands issued but
> > has to do
>
> That's different thing.  NCQ protocol doesn't require DMA SETUP FIS
> which is required for normal DMA commands but the controller still needs
> to be prepped with DMA table to know from/to where transfer data.
>
> > so only on reception of DMA setup FIS from the drive(throught ISR).
> > But in libata/ ata_qc_issue does qc prep and issue irrespective of the
> > protocol.
>
> Yeap, DMA table needs to be prepped whether NCQ is used or not.
>
> > Even i glanced thro' the sil24 driver and seems to be the same.
>
> The same for sil24.
>
> --
> tejun
>