linux-kernel - Re: [PATCH v7 4/4] sd: change to auto suspend mode

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Date:	Mon, 21 Jan 2013 20:44:14 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Aaron Lu <aaron.lu@...el.com>, Jens Axboe <axboe@...nel.dk>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Shane Huang <shane.huang@....com>
Subject: Re: [PATCH v7 4/4] sd: change to auto suspend mode

On 01/19/2013 05:25 AM, Alan Stern wrote:
> On Wed, 16 Jan 2013, Aaron Lu wrote:
>
>> From: Lin Ming<ming.m.lin@...el.com>
>>
>> Uses block layer runtime pm helper functions in
>> scsi_runtime_suspend/resume.
>> Remove scsi_autopm_* from sd open/release path and check_events path.
>> And remove the quiesce call in runtime suspend path, as we know there is
>> no request to quiesce for the device.
>>
>> Signed-off-by: Lin Ming<ming.m.lin@...el.com>
>> Signed-off-by: Aaron Lu<aaron.lu@...el.com>
>
>> --- a/drivers/scsi/scsi_sysfs.c
>> +++ b/drivers/scsi/scsi_sysfs.c
>> @@ -893,6 +893,8 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev)
>>   	 */
>>   	scsi_autopm_get_device(sdev);
>>
>> +	blk_pm_runtime_init(rq,&sdev->sdev_gendev);
>> +
>>   	error = device_add(&sdev->sdev_gendev);
>>   	if (error) {
>>   		sdev_printk(KERN_INFO, sdev,
>
> Someone just asked about the default autosuspend delay, and I realized
> your patch series doesn't set one.  Since we don't know the properties
> of the disk drive at this point (or even whether the device is a disk
> drive), the only safe course is to call
>
> 	pm_runtime_set_autosuspend_delay(&sdev->sdev_gendev, -1);
>
> before calling blk_pm_runtime_init().  Then autosuspends will be
> prevented until userspace writes a non-negative value into the device's
> control/autosuspend_delay_ms file.

OK, that would be safer, thanks for the suggestion.
I often set the autosuspend delay before allowing runtime PM for the
device, since we forbid it in scsi_sysfs_add_sdev.

>
> The kerneldoc for blk_pm_runtime_init() should mention that the caller
> needs to set the autosuspend delay beforehand.

OK.

Thanks,
Aaron
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