Re: [PATCH] libata: device suspend/resume

[Jens Axboe <axboe@suse.de>]

On Mon, May 23 2005, James Bottomley wrote:
> On Mon, 2005-05-23 at 16:45 -0400, Jeff Garzik wrote:
> > On Mon, May 23, 2005 at 03:41:15PM -0500, James Bottomley wrote:
> > > The thread petered out before a resolution, however, I think
> > > at least disk devices should be doing a synchronize cache on suspend.
> > 
> > Agreed.
> 
> OK, try this as a straw horse.  It plumbs our scsi bus model into
> suspend and resume via the driver (which would be the ULD) function.
> The only ULD which has an extra function is sd, and all it does is
> synchronize the cache if it was writeback.  I believe you translate SYNC
> CACHE in libata, so this patch should be sufficient (unless we still
> have a problem with ATA devices that lie about their cache types?)
> 
> I think this is sufficient, because if the LLD also wants this
> information, it can get it from the model of the bus it's attached to.

suspend/resume is a lot more complicated than just flushing a cache, the
below will probably get you safe asleep but you will never get devices
alive again after power-up on suspend-to-ram.

I also greatly prefer issuing a standby command to the drive after the
flush, so that we don't risk using the emergency parks of the drive. If
a drive happens to lie about wrt the flush command, it gets an extra
chance to flush the cache as it now knows that power will be gone very
soon. So I think the ->suspend/->resume hooks should belong to the LLD,
not the ULD as the ULD has no idea how to suspend all devices types.


-- 
Jens Axboe