On 7/31/23 02:39, Damien Le Moal wrote:
During system resume, ata_port_pm_resume() triggers ata EH to
1) Resume the controller
2) Reset and rescan the ports
3) Revalidate devices
This EH execution is started asynchronously from ata_port_pm_resume(),
which means that when sd_resume() is executed, none or only part of the
above processing may have been executed. However, sd_resume() issues a
START STOP UNIT to wake up the drive from sleep mode. This command is
translated to ATA with ata_scsi_start_stop_xlat() and issued to the
device. However, depending on the state of execution of the EH process
and revalidation triggerred by ata_port_pm_resume(), two things may
happen:
1) The START STOP UNIT fails if it is received before the controller has
been reenabled at the beginning of the EH execution. This is visible
with error messages like:
ata10.00: device reported invalid CHS sector 0
sd 9:0:0:0: [sdc] Start/Stop Unit failed: Result: hostbyte=DID_OK driverbyte=DRIVER_OK
sd 9:0:0:0: [sdc] Sense Key : Illegal Request [current]
sd 9:0:0:0: [sdc] Add. Sense: Unaligned write command
sd 9:0:0:0: PM: dpm_run_callback(): scsi_bus_resume+0x0/0x90 returns -5
sd 9:0:0:0: PM: failed to resume async: error -5
2) The START STOP UNIT command is received while the EH process is
on-going, which mean that it is stopped and must wait for its
completion, at which point the command is rather useless as the drive
is already fully spun up already. This case results also in a
significant delay in sd_resume() which is observable by users as
the entire system resume completion is delayed.
Given that ATA devices will be woken up by libata activity on resume,
sd_resume() has no need to issue a START STOP UNIT command, which solves
the above mentioned problems. Do not issue this command by introducing
the new scsi_device flag no_start_on_resume and setting this flag to 1
in ata_scsi_dev_config(). sd_resume() is modified to issue a START STOP
UNIT command only if this flag is not set.
Q: As libata starts up the drive internally via reset/revalidate, why do
we have to sent START STOP UNIT for shutdown?
Wouldn't it be better to disable START STOP UNIT completely for libata,
and let everything be handled via ATA command (IDLE IMMEDIATE, SLEEP) ?
Hmm?
Otherwise a really good idea. We've fallen into this trap several times
ourselves.
Incidentally, USB could benefit from the same mechanism ...
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
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Myers, Andrew McDonald, Martje Boudien Moerman
