SATA suspend/resume (was Re: [PATCH] updated version of Jens' SATA suspend-to-ram patch)

[Jeff Garzik <jgarzik@pobox.com>]

Joshua Kwan wrote:
> Hello,
>
> I had some time yesterday and decided to help Jens out by rediffing the
> now-infamous SATA suspend-to-ram patch [1] against current git and
> test-building it.
>
> For posterity,
>
> This patch adds the ata_scsi_device_resume and ata_scsi_device_suspend
> functions (along with helpers) to put to sleep and wake up Serial ATA
> controllers when entering sleep states, and hooks the functions into
> each SATA controller driver so that suspend-to-RAM is possible.
>
> Note that this patch is a holdover patch until it is possible to
> generalize this concept for all SCSI devices, which requires more data
> on which devices need to be put to sleep and which don't.
>
> Signed-off-by: Joshua Kwan <joshk@triplehelix.org>

Ah hah!  I found the other SCSI suspend patch:

	http://lwn.net/Articles/97453/

Anybody (Joshua?) up for reconciling and testing the two?

The main change from Jens/Joshua's patch is that we use SCSI's 
sd_shutdown() to call sync cache, eliminating the need for 
ata_flush_cache(), since the SCSI layer would now perform that.

For bonus points,

1) sd should call START STOP UNIT on suspend, which eliminates the need 
for ata_standby_drive(), and completely encompasses the suspend process 
in the SCSI layer.

2) sd should call START STOP UNIT on resume -- and as a SUPER BONUS, the 
combination of these two changes ensures that there are no queue 
synchronization issues, the likes of which would require hacks like 
Jens' while-loop patch.

None of these are huge changes requiring a lot of thinking/planning...

Finally, ideally, we should be issuing a hardware or software reset on 
suspend.

	Jeff


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