linux-kernel - Re: [PATCH v3 2/7] scsi: pm: use autosuspend if device supports it

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Date:	Thu, 26 Jul 2012 20:43:32 +0800
From:	Aaron Lu <aaron.lu@....com>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Jeff Garzik <jgarzik@...ox.com>, Lin Ming <minggr@...il.com>,
	Jeff Wu <jeff.wu@....com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, Aaron Lu <aaron.lwe@...il.com>
Subject: Re: [PATCH v3 2/7] scsi: pm: use autosuspend if device supports it

On Thu, Jul 26, 2012 at 12:44:24PM +0200, Oliver Neukum wrote:
> On Thursday 26 July 2012 18:05:24 Aaron Lu wrote:
> > If the device is using autosuspend, when scsi_autopm_put_device is
> > called for it, use autosuspend runtime pm calls instead of the sync
> > call.
> 
> What is the purpose of this approach?

The purpose is to let scsi layer driver(sd, sr, etc.) use the same pm
api(scsi_autopm_put_device) to put the device to runtime suspended
state.
When the device is ready to be suspended, if it does not make use of
autosuspend, call pm_runtime_put_sync for it; if it makes use of
autosuspend, call the autosuspend runtime pm apis for it.

> You need a very good reason to have an API do two different things
> based on this.

If you see the above reason not good, I'll prepare an updated version
to create a new api to cover the autosuspend case, something like:
void scsi_autopm_put_device_autosuspend(struct scsi_device *sdev)
{
	pm_runtime_mark_last_busy(&sdev->sdev_gendev);
	pm_runtime_put_autosuspend(&sdev->sdev_gendev);
}
Does this look right?

Thanks,
Aaron
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