Re: Disk wakeup on resume

[Douglas Gilbert <dgilbert@interlog.com>]

On 13-11-05 11:23 AM, Phillip Susi wrote:
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> On 11/5/2013 10:56 AM, Douglas Gilbert wrote:
>> I think that you might find that almost any SCSI command
>> (translated to its ATA equivalent command) will wake up a SATA
>> disk. Perhaps just this sequence: fd = open(<ata_bloc_device>) ;
>> close(fd) ; is sufficient.
>
> No, otherwise hdparm, udisks, etc would not be able to issue the CHECK
> POWER command without waking the disk.  Most commands do wake the
> drive, but as far as I can see, nobody is sending down any, and more
> importantly, the wake is happening within the kernel pm resume path,
> not by userspace after resume.

hdparm is quite capable of using a pass-through device
to access disks. That allows it (and smartmontools) to
access physical disks in a RAID when the block layer
can only see the logical disk out front.

udisks is not that smart.


Perhaps you need to start debugging around here:

static int sd_resume(struct device *dev)
{
         struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
         int ret = 0;

         if (!sdkp->device->manage_start_stop)
                 goto done;

         sd_printk(KERN_NOTICE, sdkp, "Starting disk\n");
         ret = sd_start_stop_device(sdkp, 1);

done:
         scsi_disk_put(sdkp);
         return ret;
}

to work out if it is spun up before or after that call.

Doug Gilbert