xhci: Blacklist using streams on the Etron EJ168 controller

Streams on the EJ168 do not work as they should. I've spend 2 days trying
to get them to work, but without success.

The first problem is that when ever you ring the stream-ring doorbell, the
controller starts executing trbs at the beginning of the first ring segment,
event if it ended somewhere else previously. This can be worked around by
allowing enqueing only one td (not a problem with how streams are typically
used) and then resetting our copies of the enqueueing en dequeueing pointers
on a td completion to match what the controller seems to be doing.

This way things seem to start working with uas and instead of being able
to complete only the very first scsi command, the scsi core can probe the disk.

But then things break later on when td-s get enqueued with more then one
trb. The controller does seem to increase its dequeue pointer while executing
a stream-ring (data transfer events I inserted for debugging do trigger).
However execution seems to stop at the final normal trb of a multi trb td,
even if there is a data transfer event inserted after the final trb.

The first problem alone is a serious deviation from the spec, and esp.
dealing with cancellation would have been very tricky if not outright
impossible, but the second problem simply is a deal breaker altogether,
so this patch simply disables streams.

Note this will cause the usb-storage + uas driver pair to automatically switch
to using usb-storage instead of uas on these devices, essentially reverting
to the 3.14 and earlier behavior when uas was marked CONFIG_BROKEN.

https://bugzilla.redhat.com/show_bug.cgi?id=1121288
https://bugzilla.kernel.org/show_bug.cgi?id=80101

Cc: stable@vger.kernel.org # 3.15
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 0342d9b63977..a0772d362e70 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -3148,7 +3148,8 @@ int xhci_alloc_streams(struct usb_hcd *hcd, struct usb_device *udev,
 			num_streams);
 
 	/* MaxPSASize value 0 (2 streams) means streams are not supported */
-	if (HCC_MAX_PSA(xhci->hcc_params) < 4) {
+	if ((xhci->quirks & XHCI_BROKEN_STREAMS) ||
+			HCC_MAX_PSA(xhci->hcc_params) < 4) {
 		xhci_dbg(xhci, "xHCI controller does not support streams.\n");
 		return -ENOSYS;
 	}