Re: [PATCH v3 2/6] usb: dwc3: gadget: cancel requests instead of release after missed isoc

Michael Grzeschik
2024-02-27T21:01:41Z

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On Thu, Feb 22, 2024 at 01:20:04AM +0000, Thinh Nguyen wrote:
>On Thu, Feb 22, 2024, Michael Grzeschik wrote:
>> For #2: I found an issue in the handling of the completion of requests in
>> the started list. When the interrupt handler is *explicitly* calling
>> stop_active_transfer if the overall event of the request was an missed
>> event. This event value only represents the value of the request that
>> was actually triggering the interrupt.
>>
>> It also calls ep_cleanup_completed_requests and is iterating over the
>> started requests and will call giveback/complete functions of the
>> requests with the proper request status.
>>
>> So this will also catch missed requests in the queue. However, since
>> there might be, lets say 5 good requests and one missed request, what
>> will happen is, that each complete call for the first good requests will
>> enqueue new requests into the started list and will also call the
>> updatecmd on that transfer that was already missed until the loop will
>> reach the one request with the MISSED status bit set.
>>
>> So in my opinion the patch from Jeff makes sense when adding the
>> following change aswell. With those both changes the underruns and
>> broken frames finally disappear. I am still unsure about the complete
>> solution about that, since with this the mentioned 5 good requests
>> will be cancelled aswell. So this is still a WIP status here.
>>
>
>When the dwc3 driver issues stop_active_transfer(), that means that the
>started_list is empty and there is an underrun.

At this moment this is only the case when both, pending and started list
are empty. Or the interrupt event was EXDEV.

The main problem is that the function
dwc3_gadget_ep_cleanup_completed_requests(dep, event, status); will
issue an complete for each started request, which on the other hand will
refill the pending list, and therefor after that refill the
stop_active_transfer is currently never hit.

>It treats the incoming requests as staled. However, for UVC, they are
>still "good".

Right, so in that case we can requeue them anyway. But this will have to
be done after the stop transfer cmd has finished.

>I think you can just check if the started_list is empty before queuing
>new requests. If it is, perform stop_active_transfer() to reschedule the
>incoming requests. None of the newly queue requests will be released
>yet since they are in the pending_list.

So that is basically exactly what my patch is doing. However in the case
of an underrun it is not safe to call dwc3_gadget_ep_cleanup_completed_requests
as jeff stated. So his underlying patch is really fixing an issue here.

>For UVC, perhaps you can introduce a new flag to usb_request called
>"ignore_queue_latency" or something equivalent. The dwc3 is already
>partially doing this for UVC. With this new flag, we can rework dwc3 to
>clearly separate the expected behavior from the function driver.

I don't know why this "extra" flag is even necessary. The code example
is already working without that extra flag.

Actually I even came up with an better solution. Additionally of checking if
one of the requests in the started list was missed, we can activly check if
the trb ring did run dry and if dwc3_gadget_endpoint_trbs_complete is
going to enqueue in to the empty trb ring.

So my whole change looks like that:

diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index efe6caf4d0e87..2c8047dcd1612 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -952,6 +952,7 @@ struct dwc3_request {
#define DWC3_REQUEST_STATUS_DEQUEUED 3
#define DWC3_REQUEST_STATUS_STALLED 4
#define DWC3_REQUEST_STATUS_COMPLETED 5
+#define DWC3_REQUEST_STATUS_MISSED_ISOC 6
#define DWC3_REQUEST_STATUS_UNKNOWN -1

u8 epnum;
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 858fe4c299b7a..a31f4d3502bd3 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2057,6 +2057,9 @@ static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
req = next_request(&dep->cancelled_list);
dwc3_gadget_ep_skip_trbs(dep, req);
switch (req->status) {
+ case 0:
+ dwc3_gadget_giveback(dep, req, 0);
+ break;
case DWC3_REQUEST_STATUS_DISCONNECTED:
dwc3_gadget_giveback(dep, req, -ESHUTDOWN);
break;
@@ -2066,6 +2069,9 @@ static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
case DWC3_REQUEST_STATUS_STALLED:
dwc3_gadget_giveback(dep, req, -EPIPE);
break;
+ case DWC3_REQUEST_STATUS_MISSED_ISOC:
+ dwc3_gadget_giveback(dep, req, -EXDEV);
+ break;
default:
dev_err(dwc->dev, "request cancelled with wrong reason:%d\n", req->status);
dwc3_gadget_giveback(dep, req, -ECONNRESET);
@@ -3509,6 +3515,36 @@ static int dwc3_gadget_ep_cleanup_completed_request(struct dwc3_ep *dep,
return ret;
}

+static int dwc3_gadget_ep_check_missed_requests(struct dwc3_ep *dep)
+{
+ struct dwc3_request *req;
+ struct dwc3_request *tmp;
+ int ret = 0;
+
+ list_for_each_entry_safe(req, tmp, &dep->started_list, list) {
+ struct dwc3_trb *trb;
+
+ trb = req->trb;
+ switch (DWC3_TRB_SIZE_TRBSTS(trb->size)) {
+ case DWC3_TRBSTS_MISSED_ISOC:
+ /* Isoc endpoint only */
+ ret = -EXDEV;
+ break;
+ case DWC3_TRB_STS_XFER_IN_PROG:
+ /* Applicable when End Transfer with ForceRM=0 */
+ case DWC3_TRBSTS_SETUP_PENDING:
+ /* Control endpoint only */
+ case DWC3_TRBSTS_OK:
+ default:
+ ret = 0;
+ break;
+ }
+ }
+
+ return ret;
+}
+
static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
const struct dwc3_event_depevt *event, int status)
{
@@ -3565,22 +3601,51 @@ static bool dwc3_gadget_endpoint_trbs_complete(struct dwc3_ep *dep,
{
struct dwc3 *dwc = dep->dwc;
bool no_started_trb = true;
+ unsigned int transfer_in_flight = 0;
+
+ /* It is possible that the interrupt thread was delayed by
+ * scheduling in the system, and therefor the HW has already
+ * run dry. In that case the last trb in the queue is already
+ * handled by the hw. By checking the HWO bit we know to restart
+ * the whole transfer. The condition to appear is more likelely
+ * if not every trb has the IOC bit set and therefor does not
+ * trigger the interrupt thread fewer.
+ */
+ if (dep->number && usb_endpoint_xfer_isoc(dep->endpoint.desc)) {
+ struct dwc3_trb *trb;

- dwc3_gadget_ep_cleanup_completed_requests(dep, event, status);
+ trb = dwc3_ep_prev_trb(dep, dep->trb_enqueue);
+ transfer_in_flight = trb->ctrl & DWC3_TRB_CTRL_HWO;
+ }

- if (dep->flags & DWC3_EP_END_TRANSFER_PENDING)
- goto out;
+ if (status == -EXDEV || !transfer_in_flight) {
+ struct dwc3_request *tmp;
+ struct dwc3_request *req;

- if (!dep->endpoint.desc)
- return no_started_trb;
+ if (!(dep->flags & DWC3_EP_END_TRANSFER_PENDING))
+ dwc3_stop_active_transfer(dep, true, true);

- if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
- list_empty(&dep->started_list) &&
- (list_empty(&dep->pending_list) || status == -EXDEV))
- dwc3_stop_active_transfer(dep, true, true);
- else if (dwc3_gadget_ep_should_continue(dep))
- if (__dwc3_gadget_kick_transfer(dep) == 0)
- no_started_trb = false;
+ list_for_each_entry_safe(req, tmp, &dep->started_list, list) {
+ dwc3_gadget_move_cancelled_request(req,
+ (DWC3_TRB_SIZE_TRBSTS(req->trb->size) == DWC3_TRBSTS_MISSED_ISOC) ?
+ DWC3_REQUEST_STATUS_MISSED_ISOC : 0);
+ }
+ } else {
+ dwc3_gadget_ep_cleanup_completed_requests(dep, event, status);
+
+ if (dep->flags & DWC3_EP_END_TRANSFER_PENDING)
+ goto out;
+
+ if (!dep->endpoint.desc)
+ return no_started_trb;
+
+ if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
+ list_empty(&dep->started_list) && list_empty(&dep->pending_list))
+ dwc3_stop_active_transfer(dep, true, true);
+ else if (dwc3_gadget_ep_should_continue(dep))
+ if (__dwc3_gadget_kick_transfer(dep) == 0)
+ no_started_trb = false;
+ }

out:
/*

I will seperate the whole hunk into smaller changes and send an v1
the next days to review.

Regards,
Michael

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