Re: SCSI:implement PM for sr

[Hannes Reinecke <hare@suse.de>]

On 01/16/2012 09:41 AM, Oliver Neukum wrote:
> From e81a6204b9c53b1e6a2817a96f0e1b44e3c87fb4 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oliver@neukum.org>
> Date: Mon, 16 Jan 2012 09:38:04 +0100
> Subject: [PATCH] SCSI:implement PM for sr
> 
> This implements basic power management for SCSI CDs.
> 
> Signed-off-by: Oliver Neukum <oneukum@suse.de>
> ---
>  drivers/scsi/sr.c |   31 +++++++++++++++++++++++++++++--
>  1 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
> index 5fc97d2..91b545b 100644
> --- a/drivers/scsi/sr.c
> +++ b/drivers/scsi/sr.c
> @@ -508,16 +508,29 @@ static int sr_prep_fn(struct request_queue *q, struct request *rq)
>  
>  static int sr_block_open(struct block_device *bdev, fmode_t mode)
>  {
> +	struct scsi_device *sdev;
>  	struct scsi_cd *cd;
>  	int ret = -ENXIO;
> +	int err;
>  
>  	mutex_lock(&sr_mutex);
>  	cd = scsi_cd_get(bdev->bd_disk);
> +	sdev = cd->device;
> +
> +	err = scsi_autopm_get_device(sdev);
> +	if (err) {
> +		ret = -EIO;
> +		goto err_out;
> +	}
> +
>  	if (cd) {
>  		ret = cdrom_open(&cd->cdi, bdev, mode);
> -		if (ret)
> +		if (ret) {
>  			scsi_cd_put(cd);
> +			scsi_autopm_put_device(sdev);
> +		}
>  	}
> +err_out:
>  	mutex_unlock(&sr_mutex);
>  	return ret;
>  }
> @@ -525,9 +538,12 @@ static int sr_block_open(struct block_device *bdev, fmode_t mode)
>  static int sr_block_release(struct gendisk *disk, fmode_t mode)
>  {
>  	struct scsi_cd *cd = scsi_cd(disk);
> +	struct scsi_device *sdev = cd->device;
> +
>  	mutex_lock(&sr_mutex);
>  	cdrom_release(&cd->cdi, mode);
>  	scsi_cd_put(cd);
> +	scsi_autopm_put_device(sdev);
>  	mutex_unlock(&sr_mutex);
>  	return 0;
>  }
> @@ -615,6 +631,11 @@ static int sr_open(struct cdrom_device_info *cdi, int purpose)
>  	struct scsi_device *sdev = cd->device;
>  	int retval;
>  
> +	retval = scsi_autopm_get_device(sdev);
> +	if (retval) {
> +		retval = -EIO;
> +		goto pm_error_out;
> +	}
>  	/*
>  	 * If the device is in error recovery, wait until it is done.
>  	 * If the device is offline, then disallow any access to it.
> @@ -626,16 +647,19 @@ static int sr_open(struct cdrom_device_info *cdi, int purpose)
>  	return 0;
>  
>  error_out:
> +	scsi_autopm_put_device(sdev);
> +pm_error_out:
>  	return retval;	
>  }
>  
>  static void sr_release(struct cdrom_device_info *cdi)
>  {
>  	struct scsi_cd *cd = cdi->handle;
> +	struct scsi_device *sdev = cd->device;
>  
>  	if (cd->device->sector_size > 2048)
>  		sr_set_blocklength(cd, 2048);
> -
> +	scsi_autopm_put_device(sdev);
>  }
>  
>  static int sr_probe(struct device *dev)
> @@ -715,6 +739,7 @@ static int sr_probe(struct device *dev)
>  	dev_set_drvdata(dev, cd);
>  	disk->flags |= GENHD_FL_REMOVABLE;
>  	add_disk(disk);
> +	scsi_autopm_put_device(sdev);
>  
>  	sdev_printk(KERN_DEBUG, sdev,
>  		    "Attached scsi CD-ROM %s\n", cd->cdi.name);
> @@ -964,7 +989,9 @@ static void sr_kref_release(struct kref *kref)
>  static int sr_remove(struct device *dev)
>  {
>  	struct scsi_cd *cd = dev_get_drvdata(dev);
> +	struct scsi_device *sdev = cd->device;
>  
> +	scsi_autopm_get_device(sdev);
>  	blk_queue_prep_rq(cd->device->request_queue, scsi_prep_fn);
>  	del_gendisk(cd->disk);
>  
Why do I have to do a _put() on probe and a _get() on remove?
This looks odd, to say the least.
Not saying it's wrong, but I would like to have a comment
here as to why the 'normal' order of _get() and _put() is
reversed here.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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