> From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb-owner@xxxxxxxxxxxxxxx] On Behalf Of Maciej Puzio > Sent: Thursday, July 17, 2014 11:25 AM > > Tested-by: Maciej Puzio <mx34567@xxxxxxxxx> > > On Tue, Jul 8, 2014 at 2:01 PM, Julius Werner <jwerner@xxxxxxxxxxxx> wrote: > > Commit 1f81b6d22 "usb: xhci: Prefer endpoint context dequeue pointer > > over stopped_trb" changed the logic in xhci_find_new_dequeue_state() to > > only use the Endpoint Context's TR Dequeue Pointer instead of the last > > Event TRB's TRB Pointer as a basis from which to infer the host > > controller state. This has uncovered a bug with certain Asmedia xHCs > > which seem to advance their TR Dequeue Pointer one TRB behind the one > > that caused a Stall Error. > > > > This confuses the cycle state calculation since cur_td->last_trb is now > > behind hw_dequeue (which the algorithm interprets as a single huge TD > > that wraps around the whole transfer ring). This patch counteracts that > > by explicitly looking for last_trb when searching for hw_dequeue from > > the old software dequeue pointer. If it is found, we toggle the cycle > > state once more to balance out the incorrect toggle that will happen > > later. > > > > In order to make this work for both single and multi segment rings, this > > patch also expands the detection of wrap-around TDs to work on the > > latter ones (which cannot normally happen because the kernel prevents > > that case to allow for ring expansion, but it's how things appear to be > > in the quirky case and allowing the code to handle it makes it easier to > > generalize this fix across all kernels). The code will now toggle the > > cycle state whenever last_trb is before hw_dequeue on the same segment, > > regardless of how many segments there are in the ring. > > > > This patch should be backported to kernels as old as 2.6.31 that contain > > the commit ae636747146ea97efa18e04576acd3416e2514f5 "USB: xhci: URB > > cancellation support." > > > > Cc: stable@xxxxxxxxxxxxxxx > > Signed-off-by: Julius Werner <jwerner@xxxxxxxxxxxx> > > --- > > drivers/usb/host/xhci-ring.c | 18 +++++++++++++----- > > 1 file changed, 13 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c > > index 749fc68..50abc68 100644 > > --- a/drivers/usb/host/xhci-ring.c > > +++ b/drivers/usb/host/xhci-ring.c > > @@ -489,8 +489,17 @@ void xhci_find_new_dequeue_state(struct xhci_hcd *xhci, > > /* Find virtual address and segment of hardware dequeue pointer */ > > state->new_deq_seg = ep_ring->deq_seg; > > state->new_deq_ptr = ep_ring->dequeue; > > + state->new_cycle_state = hw_dequeue & 0x1; > > while (xhci_trb_virt_to_dma(state->new_deq_seg, state->new_deq_ptr) > > != (dma_addr_t)(hw_dequeue & ~0xf)) { > > + /* > > + * Quirky HCs can advance hw_dequeue behind cur_td->last_trb. > > + * That violates the assumptions of the TD wrap around check > > + * below, so toggle the cycle state once more to cancel it out. > > + */ > > + if (state->new_deq_ptr == cur_td->last_trb) > > + state->new_cycle_state ^= 1; > > + > > next_trb(xhci, ep_ring, &state->new_deq_seg, > > &state->new_deq_ptr); > > if (state->new_deq_ptr == ep_ring->dequeue) { > > @@ -500,12 +509,11 @@ void xhci_find_new_dequeue_state(struct xhci_hcd *xhci, > > } > > /* > > * Find cycle state for last_trb, starting at old cycle state of > > - * hw_dequeue. If there is only one segment ring, find_trb_seg() will > > - * return immediately and cannot toggle the cycle state if this search > > - * wraps around, so add one more toggle manually in that case. > > + * hw_dequeue. If last_trb is on the current segment before hw_dequeue, > > + * that means we wrap around the whole ring, but find_trb_seq() will > > + * return immediately. Toggle the cycle state manually in that case. > > */ > > - state->new_cycle_state = hw_dequeue & 0x1; > > - if (ep_ring->first_seg == ep_ring->first_seg->next && > > + if (state->new_deq_seg->trbs < cur_td->last_trb && > > cur_td->last_trb < state->new_deq_ptr) > > state->new_cycle_state ^= 0x1; > > > > -- > > 1.8.3.2 Hmm. Wouldn't it be safer to have a quirk for this, and only enable the workaround if the Asmedia controller is detected? This code is so complicated that it is difficult to see whether this could have a harmful effect on controllers without the bug. -- Paul ��.n��������+%������w��{.n�����{���)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
