Re: [PATCH] SCSI midlayer power management

[James Bottomley <James.Bottomley@SteelEye.com>]

On Wed, 2004-08-11 at 19:36, Benjamin Herrenschmidt wrote:
> Some hosts will continuously DMA to memory iirc.. I remember having a
> problem with 53c8xx on some macs when transitionning from MacOS to Linux
> because of that.

I think you're thinking of the scripts engine?  on pre 53c875 chips,
yes, this is true.  The on-board processor is executing instructions
from host memory.  However, this is read only in quiescent (waiting for
host connect or target reconnect) mode, so shouldn't be a problem for
suspend.  On the 875 and later, we host the scripts in on-chip memory so
they shouldn't be troubling main memory when idling.

> We need to properly quisce the host, but that's a per host driver thing
> and shouldn't be too difficult.
> 
> Regarding suspend-to-disk, it's fairly easy for the sd driver not to
> spin down the disk for S4 (only for S3). However, we will still probably
> do at least a bus reset when waking up...

Why?  We don't do a bus reset on boot, why should we need to do one on
resume?  For FC, the equivalent, a LIP Reset can be rather nasty on a
SAN and should be avoided.

The slight problem is probably going to be knowing that we may need to
spin up devices (for internal ones) before resuming operation.

James