Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752400AbaGQSZa (ORCPT ); Thu, 17 Jul 2014 14:25:30 -0400 Received: from mail-ie0-f170.google.com ([209.85.223.170]:60541 "EHLO mail-ie0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751100AbaGQSZ2 (ORCPT ); Thu, 17 Jul 2014 14:25:28 -0400 MIME-Version: 1.0 In-Reply-To: <1404846104-4959-1-git-send-email-jwerner@chromium.org> References: <063D6719AE5E284EB5DD2968C1650D6D1726E25E@AcuExch.aculab.com> <1404846104-4959-1-git-send-email-jwerner@chromium.org> Date: Thu, 17 Jul 2014 13:25:28 -0500 Message-ID: Subject: Re: [PATCH] usb: xhci: Fix Set TR Dequeue Pointer cycle state for quirky xHCs From: Maciej Puzio To: Julius Werner Cc: Mathias Nyman , David Laight , Sarah Sharp , Greg Kroah-Hartman , "linux-usb@vger.kernel.org" , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Tested-by: Maciej Puzio On Tue, Jul 8, 2014 at 2:01 PM, Julius Werner 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@vger.kernel.org > Signed-off-by: Julius Werner > --- > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/