Re: [PATCH] JMicron JM20337 USB-SATA data corruption bugfix -device 152d:2338

From: Tomas Styblo
Date: Tue Jul 22 2008 - 01:11:27 EST

* Robert Hancock <hancockr@xxxxxxx> [Mon, 21 Jul 2008]:
> I'm not sure this is a good approach. More that this code right above in
> usb_stor_invoke_transport, which your code undoes the effect of for this
> device, doesn't seem right:
> /* If things are really okay, then let's show that. Zero
> * out the sense buffer so the higher layers won't realize
> * we did an unsolicited auto-sense. */
> if (result == USB_STOR_TRANSPORT_GOOD &&
> /* Filemark 0, ignore EOM, ILI 0, no sense */
> (srb->sense_buffer[2] & 0xaf) == 0 &&
> /* No ASC or ASCQ */
> srb->sense_buffer[12] == 0 &&
> srb->sense_buffer[13] == 0) {
> srb->result = SAM_STAT_GOOD;
> srb->sense_buffer[0] = 0x0;
> }

The patch doesn't exactly undo the effect of the code above,
because the value of _result_ is different. When this problem
happens, the condition above is false, _result_ is
USB_STOR_TRANSPORT_FAILED and scsi_get_resid(srb) > 0, but the
chipset doesn't report any error (NO_SENSE,ASC==0,ASCQ==0). That's
why I think there's something wrong with the chipset.

There are Windows users on various message boards who report the
same problem with this chipset - a kind of silent data corruption
that occurs only when copying large amounts of data.

But as I said I know little about SCSI and USB. I tried to locate
and fix the problem, but I can't tell whether the current error
handling code is written according to the relevant standards.

A more generic approach would certainly be better than hardcoded
device ids. Perhaps this check should be enabled for all devices?
Why not?

Tomas Styblo <tripie@xxxxxxxx>
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