linux-kernel - Re: [PATCH v2 4/4] ata: add ata port runtime PM callbacks

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Message-ID: <20111115145425.GL30922@google.com>
Date:	Tue, 15 Nov 2011 06:54:25 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <JBottomley@...allels.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	"Zhang, Rui" <rui.zhang@...el.com>
Subject: Re: [PATCH v2 4/4] ata: add ata port runtime PM callbacks

On Tue, Nov 15, 2011 at 04:51:29PM +0800, Lin Ming wrote:
> > This is not the right approach.  You should look instead at 
> > scsi_dev_type_suspend() in scsi_pm.c.  If the device is already runtime 
> > suspended then the routine should return immediately.
> 
> How about below?
> 
> diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
> index d329f8b..94b60bd 100644
> --- a/drivers/scsi/scsi_pm.c
> +++ b/drivers/scsi/scsi_pm.c
> @@ -20,6 +20,9 @@ static int scsi_dev_type_suspend(struct device *dev, pm_message_t msg)
>  	struct device_driver *drv;
>  	int err;
>  
> +	if (pm_runtime_suspended(dev))
> +		return 0;
> +

Something to be careful about is there are different types of suspend
states (PMSG_*).  IIUC, runtime PM is using PMSG_SUSPEND.  Other
states may or may not be compatible with PMSG_SUSPEND expectations, so
you can skip suspend operation if the newly requested state is
PMSG_SUSPEND but otherwise the controller needs to be woken up and
told to comply to the new state.

Thanks.

-- 
tejun
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