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

[Pawel Laszczak]

>
>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

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
>>