Re: [usb-storage] BUG: SCSI: usb storage SDHC card doesn't work in 2.6.27-rc1

Alan Stern
2008-07-30T21:29:08Z

On Wed, 30 Jul 2008, Pete Zaitcev wrote:

> On Wed, 30 Jul 2008 17:00:10 -0400 (EDT), Alan Stern <stern@rowland.harvard.edu> wrote:
>
> > +++ 2.6.26/drivers/usb/storage/transport.c
> > @@ -1034,8 +1034,21 @@ int usb_stor_Bulk_transport(struct scsi_
> > + /* Heuristically detect devices that generate bogus residues
> > + * by seeing what happens with INQUIRY and READ CAPACITY
> > + * commands.
> > + */
> > + if (bcs->Status == US_BULK_STAT_OK &&
> > + scsi_get_resid(srb) == 0 &&
> > + ((srb->cmnd[0] == INQUIRY &&
> > + transfer_length == 36) ||
> > + (srb->cmnd[0] == READ_CAPACITY &&
> > + transfer_length == 8))) {
> > + us->flags |= US_FL_IGNORE_RESIDUE;
>
> Why do you do this for INQUIRY and READ_CAPACITY only?
> Why not do it for any command?

Because those are the only two commands for which I'm reasonably
certain the device should never return a nonzero residue with Okay
status. For other commands there might be a valid positive residue --
although if there is then the device should also return Check Condition
status (the spec is unclear on this point).

Actually I'm a little concerned about the READ CAPACITY command; it's
conceivable that a removable-media device with no media present might
return a valid positive residue. However the chance of something like
that happening and causing a problem is probably sufficiently small
that we can ignore it.

Alan Stern