usb: device_next: use slist to store completed transfer requests #99672
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USBD_MAX_UDC_MSG configures the number of events coming from the UDC driver that the stack can keep. This can be filled very quickly if there would be multiple bus events for some reason, or function handlers of those events are blocked for long time. As a consequence, subsequent events could be dropped, and completed transfers not handled. To avoid it, we can store completed transfer requests in a slist and check it on every event. Signed-off-by: Johann Fischer <[email protected]>
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| /** Notification message recipient callback */ | ||
| usbd_msg_cb_t msg_cb; | ||
| /** slist to keep endpoint events */ | ||
| sys_slist_t ep_events; |
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I'm sure it was probably considered, but if not, another option is to use sys_dlist_t. There is no additional cost in storage, and list elements can be removed efficiently from any point.
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The events are processed in FIFO manner, so the advantage of "list elements can be removed efficiently from any point" doesn't seem necessary.
| if (event->type == UDC_EVT_EP_REQUEST) { | ||
| /* It has already been handled and cannot be another event type. */ | ||
| return; | ||
| } |
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I would prefer to keep the case UDC_EVT_EP_REQUEST under switch below, i.e.
case UDC_EVT_EP_REQUEST:
/* It has already been handled */
break;
Functionality wise this is equivalent to the if above, but it makes it clear that there is no omission in the switch.
| { | ||
| int err = 0; | ||
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| /* Always check if there is a completed transfer request. */ |
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Please add note that this check is really a workaround for usbd_event_carrier() dropping messages on full queue, because otherwise the reason for unconditionally calling event_handler_ep_request() is not really obvious.
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USBD_MAX_UDC_MSG configures the number of events coming from the UDC driver that the stack can keep. This can be filled very quickly if there would be multiple bus events for some reason, or function handlers of those events are blocked for long time. As a consequence, subsequent events could be dropped, and completed transfers not handled. To avoid it, we can store completed transfer requests in a slist and check it on every event.
Resolves: #74058