Re: [PATCH] usb: cdns3: remove fetched trb from cache before dequeuing

[Peter Chen]

On Thu, Nov 17, 2022 at 8:27 PM Pawel Laszczak <pawell@xxxxxxxxxxx> wrote:
>
> >
> >On Tue, Nov 15, 2022 at 6:01 PM Pawel Laszczak <pawell@xxxxxxxxxxx>
> >wrote:
> >>
> >> After doorbell DMA fetches the TRB. If during dequeuing request driver
> >> changes NORMAL TRB to LINK TRB but doesn't delete it from controller
> >> cache then controller will handle cached TRB and packet can be lost.
> >>
> >> The example scenario for this issue looks like:
> >> 1. queue request - set doorbell
> >> 2. dequeue request
> >> 3. send OUT data packet from host
> >> 4. Device will accept this packet which is unexpected 5. queue new
> >> request - set doorbell 6. Device lost the expected packet.
> >>
> >> By setting DFLUSH controller clears DRDY bit and stop DMA transfer.
> >>
> >> Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
> >> cc: <stable@xxxxxxxxxxxxxxx>
> >> Signed-off-by: Pawel Laszczak <pawell@xxxxxxxxxxx>
> >> ---
> >>  drivers/usb/cdns3/cdns3-gadget.c | 12 ++++++++++++
> >>  1 file changed, 12 insertions(+)
> >>
> >> diff --git a/drivers/usb/cdns3/cdns3-gadget.c
> >> b/drivers/usb/cdns3/cdns3-gadget.c
> >> index 5adcb349718c..ccfaebca6faa 100644
> >> --- a/drivers/usb/cdns3/cdns3-gadget.c
> >> +++ b/drivers/usb/cdns3/cdns3-gadget.c
> >> @@ -2614,6 +2614,7 @@ int cdns3_gadget_ep_dequeue(struct usb_ep *ep,
> >>         u8 req_on_hw_ring = 0;
> >>         unsigned long flags;
> >>         int ret = 0;
> >> +       int val;
> >>
> >>         if (!ep || !request || !ep->desc)
> >>                 return -EINVAL;
> >> @@ -2649,6 +2650,13 @@ int cdns3_gadget_ep_dequeue(struct usb_ep
> >*ep,
> >>
> >>         /* Update ring only if removed request is on pending_req_list list */
> >>         if (req_on_hw_ring && link_trb) {
> >> +               /* Stop DMA */
> >> +               writel(EP_CMD_DFLUSH, &priv_dev->regs->ep_cmd);
> >> +
> >> +               /* wait for DFLUSH cleared */
> >> +               readl_poll_timeout_atomic(&priv_dev->regs->ep_cmd, val,
> >> +                                         !(val & EP_CMD_DFLUSH), 1,
> >> + 1000);
> >> +
> >>                 link_trb->buffer = cpu_to_le32(TRB_BUFFER(priv_ep-
> >>trb_pool_dma +
> >>                         ((priv_req->end_trb + 1) * TRB_SIZE)));
> >>                 link_trb->control =
> >> cpu_to_le32((le32_to_cpu(link_trb->control) & TRB_CYCLE) | @@ -2660,6
> >> +2668,10 @@ int cdns3_gadget_ep_dequeue(struct usb_ep *ep,
> >>
> >>         cdns3_gadget_giveback(priv_ep, priv_req, -ECONNRESET);
> >>
> >> +       req = cdns3_next_request(&priv_ep->pending_req_list);
> >> +       if (req)
> >> +               cdns3_rearm_transfer(priv_ep, 1);
> >> +
> >
> >Why the above changes are needed?
> >
>
> Do you mean the last line or this patch?
>
> Last line:
> DMA is stopped, so driver arm the queued transfers
>

Sorry, I have been very busy recently, so the response may not be in time.
I mean why it needs to re-arm the transfers after DMA is stopped?

Peter


> If you means this patch:
> Issue was detected by customer test. I don’t know whether it was
> only test or the real application.
>
> The problem happens because user application queued the transfer
> (endpoint has been armed), so controller fetch the TRB.
> When user application removed this request the TRB was still
> processed by controller. If at that time the host will send data packet
> then controller will accept it, but it shouldn't because the usb_request
> associated with TRB cached by controller was removed.
> To force the controller to drop this TRB DFLUSH is required.
>
> Pawel
>
> >
> >>  not_found:
> >>         spin_unlock_irqrestore(&priv_dev->lock, flags);
> >>         return ret;
> >> --
> >> 2.25.1
> >>