Some people have asked me for some clarification on my request.... I hope
this message can clear up most people's questions.
Basically, there is a class of USB devices which are actually USB to SCSI
bus bridges. For most commands (such as READ_10), the bridge works very
well. We send the command, and it can determine when the full load of data
has been transported and the command has completed. However, for a command
like INQURIRY, the bridge can't really tell how much data there is to
transfer.
In these cases, the bridge begins transferring the INQUIRY data, and then
waits to see if there is any more data. The timeout built-in to these
devices (in the ASICs) is about 5 seconds (+ or - a little bit -- these are
experimentally observed numbers). After the device timeout occurs, it
concludes the transfer.
Unfortunately, with the current linux timeout of 2 seconds, the OS timeout
fires before the device timeout does. There is nothing wrong with the
command, the device, or the bridge -- the only thing we need to do is wait
longer before attempting to abort the command.
Matt Dharm
On Tue, Jun 06, 2000 at 06:52:08PM -0700, Matthew Dharm wrote:
> Can we increase the timeout for some comamnds?
>
> Specifically, some USB devices (notably the USB/SCSI bridges) which use the
> USB SCSI emulation need about 5-6 seconds to respond to an INQUIRY (as well
> as a couple of other commands).
>
> I didn't have this problem on older kernels -- I suspect that someone either
> changed the timeout or change the default debugging defines.
>
> The current timeout in 2.4.0-test1-ac8 is about 2 seconds. This is defined
> in drivers/scsi/scsi.h -- increasing this to 6 seconds works fine. Or, in
> scsi_scan.c, increase the timeout used for the probing INQUIRY command from
> the default of SCSI_TIMEOUT to 6*HZ.
>
> I can send a patch if it's desired -- but I was wondering what the
> preferred choice is.
>
> Matt Dharm
>
> --
> Matthew Dharm Home: mdharm@one-eyed-alien.net
> Senior Engineer, QCP Inc. Work: mdharm@qcpi.com
>
> Department of Justice agent. I have come to purify the flock.
> -- DOJ agent
> User Friendly, 5/22/1998
>
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-- Matthew Dharm Home: mdharm@one-eyed-alien.net Senior Engineer, QCP Inc. Work: mdharm@qcpi.comYou are needink to look more evil. You likink very strong coffee? -- Pitr to Dust Puppy User Friendly, 10/16/1998
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