On Mon, Jan 3, 2011 at 11:42 AM, Alan Stern [off-list ref] wrote:

On Mon, 3 Jan 2011, Tejun Heo wrote:

quoted

quoted

Runtime suspend should not occur unless all the child devices (i.e.,
the attached drives) are already suspended.  This means it is not
necessary to synchronize any operations, since there shouldn't be any
other accesses to the hardware going on.  Therefore there is no need to
use the error handler.

Well, it's not that simple I'm afraid.  EH actions are asynchronous.
Even if all the downstream devices are suspended, PHY events can
happen any time and EH could be active.  Hmmm... a delta but it would
make more sense to put only the controller into hot sleep while
leaving the disk alone for rotating devices.

That could be done.  How do you tell whether a particular drive is
rotational?

I don't think there is a kernel flag for it (yet).

Per ATA-8 there is flag in the identify block.

http://markmail.org/message/2vonazw4bck7nefa

As that email says, I don't know how reliable the flag is.

Greg