Hi Dan, Thanks for the comments. I've uploaded a new patch at https://lore.kernel.org/linux-usb/20231120062026.3759463-1-jchowdhary@xxxxxxxxxx/T/#u. On 11/16/23 02:09, Dan Scally wrote: > Hi Jayant, thanks for the update. I just have a couple of styling comments. > > On 09/11/2023 07:34, Jayant Chowdhary wrote: >> When we use an async work queue to perform the function of pumping >> usb requests to the usb controller, it is possible that amongst other >> factors, thread scheduling affects at what cadence we're able to pump >> requests. This could mean isoc usb requests miss their uframes - resulting >> in video stream flickers on the host device. >> >> To avoid this, we make the async_wq thread only produce isoc usb_requests >> with uvc buffers encoded into them. The process of queueing to the >> endpoint is done by the uvc_video_complete() handler. In case no >> usb_requests are ready with encoded information, we just queue a zero >> length request to the endpoint from the complete handler. >> >> For bulk endpoints the async_wq thread still queues usb requests to the >> endpoint. >> >> Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx> >> Signed-off-by: Jayant Chowdhary <jchowdhary@xxxxxxxxxx> >> Suggested-by: Avichal Rakesh <arakesh@xxxxxxxxxx> >> Suggested-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> >> --- >> Based on top of >> https://lore.kernel.org/linux-usb/20230930184821.310143-1-arakesh@xxxxxxxxxx/T/#t: >> v1->v2: Added self Signed-Off-by and addressed review comments >> v2->v3: Encode to usb requests in async_wq; queue to ep in complete handler >> for isoc transfers. >> v3->v4: Address review comments around code style. >> v4->v5: Update comments. Remove 0 length request queueing from async_wq >> thread since it is already done by the complete handler. >> v5->v6: Fix checkpatch.pl suggestions. >> >> drivers/usb/gadget/function/uvc.h | 8 + >> drivers/usb/gadget/function/uvc_video.c | 204 ++++++++++++++++++------ >> 2 files changed, 166 insertions(+), 46 deletions(-) >> >> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h >> index e8d4c87f1e09..5ff454528bd8 100644 >> --- a/drivers/usb/gadget/function/uvc.h >> +++ b/drivers/usb/gadget/function/uvc.h >> @@ -105,7 +105,15 @@ struct uvc_video { >> bool is_enabled; /* tracks whether video stream is enabled */ >> unsigned int req_size; >> struct list_head ureqs; /* all uvc_requests allocated by uvc_video */ >> + >> + /* USB requests that the video pump thread can encode into */ >> struct list_head req_free; >> + >> + /* >> + * USB requests video pump thread has already encoded into. These are >> + * ready to be queued to the endpoint. >> + */ >> + struct list_head req_ready; >> spinlock_t req_lock; >> unsigned int req_int_count; >> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c >> index 53feb790a4c3..d5311456fa8a 100644 >> --- a/drivers/usb/gadget/function/uvc_video.c >> +++ b/drivers/usb/gadget/function/uvc_video.c >> @@ -268,6 +268,100 @@ static int uvcg_video_ep_queue(struct uvc_video *video, struct usb_request *req) >> return ret; >> } >> +/* This function must be called with video->req_lock held. */ >> +static int uvcg_video_usb_req_queue(struct uvc_video *video, >> + struct usb_request *req, bool queue_to_ep) >> +{ >> + bool is_bulk = video->max_payload_size; >> + struct list_head *list = NULL; >> + >> + if (!video->is_enabled) { >> + uvc_video_free_request(req->context, video->ep); >> + return -ENODEV; >> + } >> + if (queue_to_ep) { >> + struct uvc_request *ureq = req->context; >> + /* >> + * With USB3 handling more requests at a higher speed, we can't >> + * afford to generate an interrupt for every request. Decide to >> + * interrupt: >> + * >> + * - When no more requests are available in the free queue, as >> + * this may be our last chance to refill the endpoint's >> + * request queue. >> + * >> + * - When this is request is the last request for the video >> + * buffer, as we want to start sending the next video buffer >> + * ASAP in case it doesn't get started already in the next >> + * iteration of this loop. >> + * >> + * - Four times over the length of the requests queue (as >> + * indicated by video->uvc_num_requests), as a trade-off >> + * between latency and interrupt load. >> + */ >> + if (list_empty(&video->req_free) || ureq->last_buf || >> + !(video->req_int_count % >> + DIV_ROUND_UP(video->uvc_num_requests, 4))) { >> + video->req_int_count = 0; >> + req->no_interrupt = 0; >> + } else { >> + req->no_interrupt = 1; >> + } >> + video->req_int_count++; >> + return uvcg_video_ep_queue(video, req); >> + } >> + /* >> + * If we're not queuing to the ep, for isoc we're queuing >> + * to the req_ready list, otherwise req_free. >> + */ >> + list = is_bulk ? &video->req_free : &video->req_ready; >> + list_add_tail(&req->list, list); >> + return 0; >> +} >> + >> +/* >> + * Must only be called from uvcg_video_enable - since after that we only want to >> + * queue requests to the endpoint from the uvc_video_complete complete handler. >> + * This function is needed in order to 'kick start' the flow of requests from >> + * gadget driver to the usb controller. >> + */ >> +static void uvc_video_ep_queue_initial_requests(struct uvc_video *video) >> +{ >> + struct usb_request *req = NULL; >> + unsigned long flags = 0; >> + unsigned int count = 0; >> + int ret = 0; > Add an empty line here please Done. >> + /* >> + * We only queue half of the free list since we still want to have >> + * some free usb_requests in the free list for the video_pump async_wq >> + * thread to encode uvc buffers into. Otherwise we could get into a >> + * situation where the free list does not have any usb requests to >> + * encode into - we always end up queueing 0 length requests to the >> + * end point. >> + */ >> + unsigned int half_list_size = video->uvc_num_requests / 2; >> + >> + spin_lock_irqsave(&video->req_lock, flags); >> + /* >> + * Take these requests off the free list and queue them all to the >> + * endpoint. Since we queue 0 length requests with the req_lock held, >> + * there isn't any 'data' race involved here with the complete handler. >> + */ >> + while (count < half_list_size) { >> + req = list_first_entry(&video->req_free, struct usb_request, >> + list); >> + list_del(&req->list); >> + req->length = 0; >> + ret = uvcg_video_ep_queue(video, req); >> + if (ret < 0) { >> + uvcg_queue_cancel(&video->queue, /*disconnect*/0); > > > Drop the /*disconnect*/ comment please Done. > >> + break; >> + } >> + count++; >> + } >> + spin_unlock_irqrestore(&video->req_lock, flags); >> +} >> + >> static void >> uvc_video_complete(struct usb_ep *ep, struct usb_request *req) >> { >> @@ -276,6 +370,8 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req) >> struct uvc_video_queue *queue = &video->queue; >> struct uvc_buffer *last_buf = NULL; >> unsigned long flags; >> + bool is_bulk = video->max_payload_size; >> + int ret = 0; >> spin_lock_irqsave(&video->req_lock, flags); >> if (!video->is_enabled) { >> @@ -329,8 +425,46 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req) >> * back to req_free >> */ >> if (video->is_enabled) { >> - list_add_tail(&req->list, &video->req_free); >> - queue_work(video->async_wq, &video->pump); >> + /* >> + * Here we check whether any request is available in the ready >> + * list. If it is, queue it to the ep and add the current >> + * usb_request to the req_free list - for video_pump to fill in. >> + * Otherwise, just use the current usb_request to queue a 0 >> + * length request to the ep. Since we always add to the req_free >> + * list if we dequeue from the ready list, there will never >> + * be a situation where the req_free list is completely out of >> + * requests and cannot recover. >> + */ >> + struct usb_request *to_queue = req; >> + >> + to_queue->length = 0; >> + if (!list_empty(&video->req_ready)) { >> + to_queue = list_first_entry(&video->req_ready, >> + struct usb_request, list); >> + list_del(&to_queue->list); >> + /* Add it to the free list. */ > I would drop the "Add it to the free list" comment; the code is clear already. Done. >> + list_add_tail(&req->list, &video->req_free); >> + /* >> + * Queue work to the wq as well since it is possible that a >> + * buffer may not have been completely encoded with the set of >> + * in-flight usb requests for whih the complete callbacks are >> + * firing. >> + * In that case, if we do not queue work to the worker thread, >> + * the buffer will never be marked as complete - and therefore >> + * not be returned to userpsace. As a result, >> + * dequeue -> queue -> dequeue flow of uvc buffers will not >> + * happen. >> + */ >> + queue_work(video->async_wq, &video->pump); >> + } >> + /* >> + * Queue to the endpoint. The actual queueing to ep will >> + * only happen on one thread - the async_wq for bulk endpoints >> + * and this thread for isoc endpoints. >> + */ >> + ret = uvcg_video_usb_req_queue(video, to_queue, !is_bulk); >> + if (ret < 0) >> + uvcg_queue_cancel(queue, 0); >> } else { >> uvc_video_free_request(ureq, ep); >> } >> @@ -347,6 +481,7 @@ uvc_video_free_requests(struct uvc_video *video) >> INIT_LIST_HEAD(&video->ureqs); >> INIT_LIST_HEAD(&video->req_free); >> + INIT_LIST_HEAD(&video->req_ready); >> video->req_size = 0; >> return 0; >> } >> @@ -424,8 +559,7 @@ static void uvcg_video_pump(struct work_struct *work) >> struct usb_request *req = NULL; >> struct uvc_buffer *buf; >> unsigned long flags; >> - bool buf_done; >> - int ret; >> + int ret = 0; >> while (true) { >> if (!video->ep->enabled) >> @@ -454,15 +588,6 @@ static void uvcg_video_pump(struct work_struct *work) >> if (buf != NULL) { >> video->encode(req, video, buf); >> - buf_done = buf->state == UVC_BUF_STATE_DONE; >> - } else if (!(queue->flags & UVC_QUEUE_DISCONNECTED) && !is_bulk) { >> - /* >> - * No video buffer available; the queue is still connected and >> - * we're transferring over ISOC. Queue a 0 length request to >> - * prevent missed ISOC transfers. >> - */ >> - req->length = 0; >> - buf_done = false; >> } else { >> /* >> * Either the queue has been disconnected or no video buffer >> @@ -473,45 +598,25 @@ static void uvcg_video_pump(struct work_struct *work) >> break; >> } >> - /* >> - * With USB3 handling more requests at a higher speed, we can't >> - * afford to generate an interrupt for every request. Decide to >> - * interrupt: >> - * >> - * - When no more requests are available in the free queue, as >> - * this may be our last chance to refill the endpoint's >> - * request queue. >> - * >> - * - When this is request is the last request for the video >> - * buffer, as we want to start sending the next video buffer >> - * ASAP in case it doesn't get started already in the next >> - * iteration of this loop. >> - * >> - * - Four times over the length of the requests queue (as >> - * indicated by video->uvc_num_requests), as a trade-off >> - * between latency and interrupt load. >> - */ >> - if (list_empty(&video->req_free) || buf_done || >> - !(video->req_int_count % >> - DIV_ROUND_UP(video->uvc_num_requests, 4))) { >> - video->req_int_count = 0; >> - req->no_interrupt = 0; >> - } else { >> - req->no_interrupt = 1; >> - } >> - >> - /* Queue the USB request */ >> - ret = uvcg_video_ep_queue(video, req); >> spin_unlock_irqrestore(&queue->irqlock, flags); >> + spin_lock_irqsave(&video->req_lock, flags); >> + /* For bulk end points we queue from the worker thread >> + * since we would preferably not want to wait on requests >> + * to be ready, in the uvcg_video_complete() handler. >> + * For isoc endpoints we add the request to the ready list >> + * and only queue it to the endpoint from the complete handler. >> + */ >> + ret = uvcg_video_usb_req_queue(video, req, is_bulk); >> + spin_unlock_irqrestore(&video->req_lock, flags); >> + >> if (ret < 0) { >> uvcg_queue_cancel(queue, 0); >> break; >> } >> - /* Endpoint now owns the request */ >> + /* The request is owned by the endpoint / ready list. */ >> req = NULL; >> - video->req_int_count++; >> } >> if (!req) >> @@ -567,7 +672,7 @@ uvcg_video_disable(struct uvc_video *video) >> spin_lock_irqsave(&video->req_lock, flags); >> /* >> - * Remove all uvc_reqeusts from ureqs with list_del_init >> + * Remove all uvc_requests from ureqs with list_del_init > > Did the alignment of the * get messed up here as well as the typo fix or is it just my mail client being weird? > I think the alignment did indeed get messed up. Fixed. Thank you, Jayant
