Re: sata_nv + ADMA + Samsung disk problem

[Mark Lord <lkml@rtr.ca>]

Robert Hancock wrote:
..
>  From some of the traces I took previously (posted on LKML as "sata_nv 
> ADMA controller lockup investigation" way back in Feb 07), what seems to 
> occur is that when the second command is issued very rapidly (within 
> less than 20 microseconds, or potentially longer) after the previous 
> command's completion, the ADMA status changes from 0x500 (STOPPED and 
> IDLE) to 0x400 (just IDLE) as it typically does, but then it sticks 
> there, no interrupt is ever raised, and CPB response flags remain at 0.
..

Assuming that NVidia got their ADMA core logic from Pacific Digital
(the inventors), then it may have some of the same bugs as the original.

One of those bugs is that the aGO trigger is sampled in a "racey" way,
such that it sometimes may miss a recent addition to the ring.

The *only* way to guarantee things with the original Pacific Digital core
was to (1) always retrigger aGO for a full ring scan with each new addition,
and (2) poll periodically (every half second or so) rather than relying
exclusively on the IRQ actually working..

Dunno about the NVidia version.

Cheers