Re: [PATCH] scsi: sd: add runtime pm to open / release

Bart Van Assche
2020-06-24T13:33:26Z

On 2020-06-23 04:10, Martin Kepplinger wrote:
> This add a very conservative but simple implementation for runtime PM
> to the sd scsi driver:
> Resume when opened (mounted) and suspend when released (unmounted).
>
> Improvements that allow suspending while a device is "open" can
> be added later, but now we save power when no filesystem is mounted
> and runtime PM is enabled.
>
> Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
> ---
> drivers/scsi/sd.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index d90fefffe31b..fe4cb7c50ec1 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -1372,6 +1372,7 @@ static int sd_open(struct block_device *bdev, fmode_t mode)
> SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_open\n"));
>
> sdev = sdkp->device;
> + scsi_autopm_get_device(sdev);
>
> /*
> * If the device is in error recovery, wait until it is done.
> @@ -1418,6 +1419,9 @@ static int sd_open(struct block_device *bdev, fmode_t mode)
>
> error_out:
> scsi_disk_put(sdkp);
> +
> + scsi_autopm_put_device(sdev);
> +
> return retval;
> }
>
> @@ -1441,6 +1445,8 @@ static void sd_release(struct gendisk *disk, fmode_t mode)
>
> SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_release\n"));
>
> + scsi_autopm_put_device(sdev);
> +
> if (atomic_dec_return(&sdkp->openers) == 0 && sdev->removable) {
> if (scsi_block_when_processing_errors(sdev))
> scsi_set_medium_removal(sdev, SCSI_REMOVAL_ALLOW);

My understanding of the above patch is that it introduces a regression,
namely by disabling runtime suspend as long as an sd device is held open.

Bart.