scsi: sd: Differentiate system and runtime start/stop management
The underlying device and driver of a SCSI disk may have different system and runtime power mode control requirements. This is because runtime power management affects only the SCSI disk, while system level power management affects all devices, including the controller for the SCSI disk. For instance, issuing a START STOP UNIT command when a SCSI disk is runtime suspended and resumed is fine: the command is translated to a STANDBY IMMEDIATE command to spin down the ATA disk and to a VERIFY command to wake it up. The SCSI disk runtime operations have no effect on the ata port device used to connect the ATA disk. However, for system suspend/resume operations, the ATA port used to connect the device will also be suspended and resumed, with the resume operation requiring re-validating the device link and the device itself. In this case, issuing a VERIFY command to spinup the disk must be done before starting to revalidate the device, when the ata port is being resumed. In such case, we must not allow the SCSI disk driver to issue START STOP UNIT commands. Allow a low level driver to refine the SCSI disk start/stop management by differentiating system and runtime cases with two new SCSI device flags: manage_system_start_stop and manage_runtime_start_stop. These new flags replace the current manage_start_stop flag. Drivers setting the manage_start_stop are modifed to set both new flags, thus preserving the existing start/stop management behavior. For backward compatibility, the old manage_start_stop sysfs device attribute is kept as a read-only attribute showing a value of 1 for devices enabling both new flags and 0 otherwise. Fixes: 0a858905 ("ata,scsi: do not issue START STOP UNIT on resume") Cc: stable@vger.kernel.org Signed-off-by:Damien Le Moal <dlemoal@kernel.org> Reviewed-by: