On Mon, Dec 19, 2011 at 12:12:26PM -0800, Sarah Sharp wrote: > On Mon, Dec 19, 2011 at 02:50:50PM -0500, Matthew Wilcox wrote: > > On Mon, Dec 19, 2011 at 08:39:55PM +0100, Sebastian Andrzej Siewior wrote: > > > In "usb/uas: use unique tags for all LUNs" we make sure to create unique > > > tags across all LUNs. This patch uses scsi_host_find_tag() to obtain the > > > correct command which is associated with the tag. > > > The following changes were required: > > > - don't use sdev->current_cmnd anymore > > > Since be can have devices which don't support command tagging we must > > > ensure that we can tell the two commands apart. devinfo->cmnd is used > > > for this. > > > > I don't understand. There's one devinfo per sdev. How does moving the > > untagged command anchor from sdev to devinfo change anything? > > I thought there was only one devinfo per USB device. uas_probe() is > only called once per USB device, and that's where devinfo is allocated and > the scsi_host is created. Oh, duh, there's one devinfo per Scsi_Host. Sorry, my mistake. > > It's my understanding that the SCSI core will only send either a single > > untagged command, or tagged commands. ie any outstanding tagged command > > will cause an untagged command to be deferred, and an outstanding untagged > > command will prevent any other command from being sent to the driver. > > Across all scsi_devices on a scsi_host? Per scsi_dev ... which of course is insufficient ... > In the status command completion for USB 2.0 devices, we can't know > which scsi_device we're completing the command for. Is it an untagged > command completion for LUN 1 or LUN 2? We can't tell, because the > device could reorder the commands across LUNs. So for untagged USB 2.0 > devices, we need to be sure there is only one untagged command pending > per scsi_host, and pull the command out of devinfo. Yes, makes sense now :-) So we can have multiple tagged commands to LUN 2 and a single untagged command to LUN 1, which is just fine. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
