scsi: core: allow auto suspend override by low-level driver

Rework from previous work by:
Sujit Reddy Thumma <sthumma@codeaurora.org>

Until now the scsi mid-layer forbids runtime suspend till userspace enables
it. This is mainly to quarantine some disks with broken runtime power
management or have high latencies executing suspend resume callbacks. If
the userspace doesn't enable the runtime suspend the underlying hardware
will be always on even when it is not doing any useful work and thus
wasting power.

Some low-level drivers for the controllers can efficiently use runtime
power management to reduce power consumption and improve battery life.
Allow runtime suspend parameters override within the LLD itself instead of
waiting for userspace to control the power management.

Link: https://lore.kernel.org/r/1568649411-5127-2-git-send-email-stanley.chu@mediatek.comReviewed-by: Avri Altman <avri.altman@wdc.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_sysfs.c

@@ -1300,6 +1300,7 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev)
 	device_enable_async_suspend(&sdev->sdev_gendev);
 	scsi_autopm_get_target(starget);
 	pm_runtime_set_active(&sdev->sdev_gendev);
+	if (!sdev->rpm_autosuspend)
 		pm_runtime_forbid(&sdev->sdev_gendev);
 	pm_runtime_enable(&sdev->sdev_gendev);
 	scsi_autopm_put_target(starget);

drivers/scsi/sd.c

@@ -3367,6 +3367,10 @@ static int sd_probe(struct device *dev)
 	}
 
 	blk_pm_runtime_init(sdp->request_queue, dev);
+	if (sdp->rpm_autosuspend) {
+		pm_runtime_set_autosuspend_delay(dev,
+			sdp->host->hostt->rpm_autosuspend_delay);
+	}
 	device_add_disk(dev, gd, NULL);
 	if (sdkp->capacity)
 		sd_dif_config_host(sdkp);

include/scsi/scsi_device.h

@@ -199,7 +199,8 @@ struct scsi_device {
 	unsigned broken_fua:1;		/* Don't set FUA bit */
 	unsigned lun_in_cdb:1;		/* Store LUN bits in CDB[1] */
 	unsigned unmap_limit_for_ws:1;	/* Use the UNMAP limit for WRITE SAME */
-
+	unsigned rpm_autosuspend:1;	/* Enable runtime autosuspend at device
+					 * creation time */
 	atomic_t disk_events_disable_depth; /* disable depth for disk events */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */

include/scsi/scsi_host.h

@@ -486,6 +486,9 @@ struct scsi_host_template {
 	 */
 	unsigned int cmd_size;
 	struct scsi_host_cmd_pool *cmd_pool;
+
+	/* Delay for runtime autosuspend */
+	int rpm_autosuspend_delay;
 };
 
 /*