[PATCH 3.12 61/82] Revert "usb: xhci: Link TRB must not occur within a USB payload burst"

Greg Kroah-Hartman
2014-02-21T00:29:09Z

From: Sarah Sharp <sarah.a.sharp@linux.intel.com>

commit 3d4b81eda2211f32886e2978daf6f39885042fc4 upstream.

This reverts commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e. It's a
hack that caused regressions in the usb-storage and userspace USB
drivers that use usbfs and libusb. Commit 70cabb7d992f "xhci 1.0: Limit
arbitrarily-aligned scatter gather." should fix the issues seen with the
ax88179_178a driver on xHCI 1.0 hosts, without causing regressions.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/host/xhci-ring.c | 54 +------------------------------------------
include/linux/usb.h | 2 -
2 files changed, 2 insertions(+), 54 deletions(-)

--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2929,58 +2929,8 @@ static int prepare_ring(struct xhci_hcd
}

while (1) {
- 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 (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");
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1262,8 +1262,6 @@ typedef void (*usb_complete_t)(struct ur
* @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