Re: Suspend issues with a LaCie USB hard disk connected

Daniel Mack
2014-01-15T17:29:32Z

Hi Alan,

On 01/15/2014 06:19 PM, Alan Stern wrote:
> On Wed, 15 Jan 2014, Daniel Mack wrote:
>
>> Hi,
>>
>> Sorry for the long, primarily holiday-related delay on this.
>>
>> On 12/18/2013 09:46 PM, Alan Stern wrote:
>>> On Wed, 18 Dec 2013, Daniel Mack wrote:
>>>> I'm facing an issue putting an embedded system to sleep while a Lacie
>>>> external USB hard disk is connected. Relevant kernel messages that occur
>>>> at the attempt are:
>>>>
>>>> [ 13.834731] PM: Sending message for entering DeepSleep mode
>>>> [ 13.846575] sd 0:0:0:0: [sda] Synchronizing SCSI cache
>>>> [ 13.858818] sd 0:0:0:0: [sda]
>>>> [ 13.862432] Result: hostbyte=0x00 driverbyte=0x08
>>>> [ 13.867349] sd 0:0:0:0: [sda]
>>>> [ 13.870626] Sense Key : 0x5 [current]
>>>> [ 13.874602] sd 0:0:0:0: [sda]
>>>> [ 13.877879] ASC=0x20 ASCQ=0x0
>>>> [ 13.885053] dpm_run_callback(): scsi_bus_suspend+0x0/0x20 returns -5
>>>> [ 13.901130] PM: Device 0:0:0:0 failed to suspend async: error -5
>>>> [ 13.907507] PM: Some devices failed to suspend, or early wake event
>>>> detected
>>>>
>>>> What happens is that in sd_sync_cache(), scsi_execute_req_flags()
>>>> returns 0x08000002, so driver_byte(res) evaluates to DRIVER_SENSE and
>>>> host_byte(res) is DID_OK, which is an unhandled case that leads to -EIO
>>>> eventually.
>>>>
>>>> I have admittedly not much clue about the SCSI layer, so I wonder what
>>>> would be the best way to fix this. Should DID_OK just be handled as
>>>> non-error condition in the switch? Should the suspend call chain ignore
>>>> such errors from sd_sync_cache()?
>>>>
>>>> I'm open to suggestions and happy to test patches.
>>>
>>> The Sense Key and ASC values indicate that the drive did not understand
>>> the SYNCHRONIZE CACHE command. A usbmon trace would verify this; see
>>> the instructions in Documentation/usb/usbmon.txt.
>>>
>>> Assuming that really is what happened, we have to decide how to handle
>>> the situation.
>>
>> Ok, this is the usbmon trace that I captured when the system goes to
>> suspend with the USB storage media connected but unmounted:
>>
>> cebe5e00 3629314504 S Bo:1:003:2 -115 31 = 55534243 10000000 00000000
>> 00000a35 00000000 00000000 00000000 000000
>> cebe5e00 3629315214 C Bo:1:003:2 0 31 >
>> cebe5e00 3629315413 S Bi:1:003:1 -115 13 <
>> cebe5e00 3629315492 C Bi:1:003:1 0 13 = 55534253 10000000 00000000 01
>
> That's the SYNCHRONIZE CACHE command, with an error return status.
>
>> cebe5e00 3629315571 S Bo:1:003:2 -115 31 = 55534243 11000000 12000000
>> 80000603 00000012 00000000 00000000 000000
>> cebe5e00 3629315606 C Bo:1:003:2 0 31 >
>> cecd4580 3629315681 S Bi:1:003:1 -115 18 <
>> cecd4580 3629315744 C Bi:1:003:1 0 18 = 70000500 0000000a 00000000
>> 20000000 0000
>> cebe5e00 3629315772 S Bi:1:003:1 -115 13 <
>> cebe5e00 3629315817 C Bi:1:003:1 0 13 = 55534253 11000000 00000000 00
>
> And that's the sense data, confirming SK=5 and ASC=20. This means the
> drive doesn't understand the command.

Ok.

> There's more stuff later on in the usbmon trace that I don't
> understand. But if everything else works okay, it won't matter.

The host controller tried to reset the port and the device, whatever
that results in. You're right, that is unrelated.

> I don't think that is the right thing to do. Try this patch instead.

[...]

> Index: usb-3.13/drivers/scsi/sd.c
> ===================================================================
> --- usb-3.13.orig/drivers/scsi/sd.c
> +++ usb-3.13/drivers/scsi/sd.c
> @@ -1463,8 +1463,8 @@ static int sd_sync_cache(struct scsi_dis
> sd_print_sense_hdr(sdkp, &sshdr);
> /* we need to evaluate the error return */
> if (scsi_sense_valid(&sshdr) &&
> - /* 0x3a is medium not present */
> - sshdr.asc == 0x3a)
> + (sshdr.asc == 0x3a || /* medium not present */
> + sshdr.asc == 0x20)) /* invalid command */
> /* this is no error here */
> return 0;
>

That seems to work equally well for me, thanks!

Feel free to add when submitting:

Reported-by: Sven Neumann <s.neumann@raumfeld.com>
Tested-by: Daniel Mack <zonque@gmail.com>

Thanks for your help!
Daniel