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-rw-r--r--drivers/usb/host/xhci-ring.c54
-rw-r--r--include/linux/usb.h2
2 files changed, 54 insertions, 2 deletions
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 1e2f3f495843..53c2e296467f 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2973,8 +2973,58 @@ static int prepare_ring(struct xhci_hcd *xhci, struct xhci_ring *ep_ring,
}
while (1) {
- if (room_on_ring(xhci, ep_ring, num_trbs))
- break;
+ if (room_on_ring(xhci, ep_ring, num_trbs)) {
+ union xhci_trb *trb = ep_ring->enqueue;
+ unsigned int usable = ep_ring->enq_seg->trbs +
+ TRBS_PER_SEGMENT - 1 - trb;
+ u32 nop_cmd;
+
+ /*
+ * Section 4.11.7.1 TD Fragments states that a link
+ * TRB must only occur at the boundary between
+ * data bursts (eg 512 bytes for 480M).
+ * While it is possible to split a large fragment
+ * we don't know the size yet.
+ * Simplest solution is to fill the trb before the
+ * LINK with nop commands.
+ */
+ if (num_trbs == 1 || num_trbs <= usable || usable == 0)
+ break;
+
+ if (ep_ring->type != TYPE_BULK)
+ /*
+ * While isoc transfers might have a buffer that
+ * crosses a 64k boundary it is unlikely.
+ * Since we can't add NOPs without generating
+ * gaps in the traffic just hope it never
+ * happens at the end of the ring.
+ * This could be fixed by writing a LINK TRB
+ * instead of the first NOP - however the
+ * TRB_TYPE_LINK_LE32() calls would all need
+ * changing to check the ring length.
+ */
+ break;
+
+ if (num_trbs >= TRBS_PER_SEGMENT) {
+ xhci_err(xhci, "Too many fragments %d, max %d\n",
+ num_trbs, TRBS_PER_SEGMENT - 1);
+ return -ENOMEM;
+ }
+
+ nop_cmd = cpu_to_le32(TRB_TYPE(TRB_TR_NOOP) |
+ ep_ring->cycle_state);
+ ep_ring->num_trbs_free -= usable;
+ do {
+ trb->generic.field[0] = 0;
+ trb->generic.field[1] = 0;
+ trb->generic.field[2] = 0;
+ trb->generic.field[3] = nop_cmd;
+ trb++;
+ } while (--usable);
+ ep_ring->enqueue = trb;
+ if (room_on_ring(xhci, ep_ring, num_trbs))
+ break;
+ }
if (ep_ring == xhci->cmd_ring) {
xhci_err(xhci, "Do not support expand command ring\n");
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 7454865ad148..512ab162832c 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1264,6 +1264,8 @@ typedef void (*usb_complete_t)(struct urb *);
* @sg: scatter gather buffer list, the buffer size of each element in
* the list (except the last) must be divisible by the endpoint's
* max packet size if no_sg_constraint isn't set in 'struct usb_bus'
+ * (FIXME: scatter-gather under xHCI is broken for periodic transfers.
+ * Do not use urb->sg for interrupt endpoints for now, only bulk.)
* @num_mapped_sgs: (internal) number of mapped sg entries
* @num_sgs: number of entries in the sg list
* @transfer_buffer_length: How big is transfer_buffer. The transfer may