Re: [PATCH v3 3/6] [SCSI] runtime resume device before system suspend

On Thu, 24 Nov 2011, Tejun Heo wrote:

Hello,

On Thu, Nov 24, 2011 at 2:54 PM, Alan Stern [off-list ref] wrote:

quoted

Therefore, when entering the SUSPEND or HIBERNATE stages of system
sleep, we can skip the callback to the driver if the device is already
in runtime suspend. �When entering the FREEZE stage, however, we should
first issue a runtime resume. �The overhead of doing this is
negligible, because a suspended drive would be spun up during the THAW
stage of hibernation anyway.

My brain is half fried at the moment so maybe you're saying the same
thing, but I hope this is something simple. Like...

    /* for libata runtime suspend is equivalent to suspend */
    if (runtime suspended && target == SUSPEND) {
        yeah! skip drive pm ops;
    } else {
        end runtime pm;
        ask EH to enter target PM state;
    }

Almost.  More like this:

	/*
	 * sd is the only high-level SCSI driver to implement runtime 
	 * PM, and sd treats runtime suspend, system suspend, and 
	 * system hibernate identically (but not system freeze).
	 */
	if (runtime-suspended) {
		if (target == SUSPEND || target == HIBERNATE)
			return 0;	/* already suspended */
		/* wake up device so that FREEZE will succeed */
		pm_runtime_resume();
	}
	tell device driver to enter target PM state

libata does not contain the SCSI device driver; it contains the host
driver.

I really don't think we need to optimize this further than this.

The above has two lines (plus comments) of optimization.  Okay?

Alan Stern