On Fri, 7 Nov 2003, Dmitri Katchalov wrote:
> Greetings,
>
> I finally managet to get Sony DCR-TRV17E memory stick
> working with usb-storage.
> The solution turned out to be very simple:
>
> echo "Sony:Sony DSC:0" > /proc/scsi/device_info
>
> But I'm puzzled as to why didn't it work in the first
> place despite several reports to the contrary. My guess
> is it used to work in earlier kernels and then some
> seemingly unrelated change broke it.
>
> I investigated it a little and that's what I found:
> This device uses CB transport (SENSE status not reported).
> This device does not support MODE_SENSE at all.
> MODE_SENSE(6) fails with STALL condition. Subsequent
> REQUEST-SENSE reports ILLEGAL REQUEST. SCSI layer is
> able to handle this situation, the only drawback is
> that write-protect status is not reported.
>
> Unfortunately usb-storage sets use_10_for_ms flag
> by default which causes SCSI to try MODE_SENSE(10)
> first.
> The device responds to MODE_SENSE(10) with "babble"
> (-EOVERFLOW). scsiglue sees transport error and
> tries to do a soft reset (which also fails).
> Note that scsiglue does not automatically send
> REQUEST-SENSE in this case.
>
> scsiglue then gives up after several attempts and
> reports the error to the upper layer. Upper layer
> (SCSI) correctly realises that MODE_SENSE(10) does
> not work and attempts to fallback to MODE_SENSE(6)
> but before that it issues TEST_UNIT_READY.
>
> This time the device responds with ILLEGAL REQUEST.
> Now SCSI gets totally confused and decides to give up.
>
> As I understand it this ILLEGAL REQUEST actually refers
> to the previous MODE_SENSE(10) command because this
> error condition has never been cleared properly.
You're probably right. But that's not how TEST-UNIT-READY is _supposed_
to behave. It shouldn't be reporting the status from a previous command;
it should indicate the device's current status.
> If I change interpret_usb_result() in transport.c
> to ignore "babble" then the next REQUEST-SENSE
> reports ILLEGAL REQUEST, SCSI handles that and
> everything sort of works.
>
> Regards,
> Dmitri
Patrick, what do you think about implementing that change to have the
response checker retry when it gets ILLEGAL REQUEST from a
TEST-UNIT-READY?
Alan Stern
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