> >hi Pawel Laszczak > >Recently, I met the problem when use uvc. UVC report jpg header error. > >Basic reproduce steps. >Gadget side: >1 - > https://urldefense.com/v3/__https://gist.github.com/kbingham/c39c >4cc7c20882a104c08df5206e2f9f?permalink_comment_id=3270713__;!!EHscm >S1ygiU1lA!H1h8GlLnbS6vqklXm_2qGyinP638O62Kk2eLB9zeMkjAGXUAPYyPXDL >FasSqYt16xq0RGT0Ff-cP4A$ > uvc-gadget.sh start >2 - > https://urldefense.com/v3/__https://git.ideasonboard.org/uvc- >gadget.git__;!!EHscmS1ygiU1lA!H1h8GlLnbS6vqklXm_2qGyinP638O62Kk2eLB9z >eMkjAGXUAPYyPXDLFasSqYt16xq0RGT1ogOdRQA$ > uvc-gadget -i test.jpg > > >Host side: > https://urldefense.com/v3/__https://github.com/thekvs/uvccapture2 >__;!!EHscmS1ygiU1lA!H1h8GlLnbS6vqklXm_2qGyinP638O62Kk2eLB9zeMkjAGX >UAPYyPXDLFasSqYt16xq0RGT1MNlKiXA$ > uvccapture2 --device /dev/video0 --resolution 640x360 --count 1 -- >result 8qxp.jpeg > > It will report jpeg header error. > > >After debugs, I found two problem. > >Problem 1, sg is enabled. so uvc driver will use sg. each package include two >trb, trb0 is 8bytes header, trb1 is 1016bytes. total 1024. > >num_trb here is wrong. >it should be > num_trb = priv_ep->interval * request->num_mapped_sgs. > >because priv_ep->interval is 1, I just simple set to request->num_mapped_sg >as below patch. USB analyer show one whole 1024 ISO package sent out as >expectation although document said only support one TD when use ISO >(Maybe my doc is too old). Support for sg in uvc has been added after upstreaming this driver, so the driver needs some improvement. Calculating of num_trb probably will more complicated change. You can see how it is implemented in https://elixir.bootlin.com/linux/latest/source/drivers/usb/gadget/udc/cdns2/cdns2-gadget.c#L412. CDNS2 is different controller and support only HS but has borrowed the DMA part from CDNS3. It was upsteamed after adding sg to UVC. Regarding TD, it is true that controller can support only one TD per SOF but this TD can contain many TRBs > >diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3- >gadget.c >index 69a44bd7e5d02..8cc99a885883f 100644 >--- a/drivers/usb/cdns3/cdns3-gadget.c >+++ b/drivers/usb/cdns3/cdns3-gadget.c >@@ -1125,10 +1125,7 @@ static int cdns3_ep_run_transfer(struct >cdns3_endpoint *priv_ep, > struct scatterlist *s = NULL; > bool sg_supported = !!(request->num_mapped_sgs); > >- if (priv_ep->type == USB_ENDPOINT_XFER_ISOC) >- num_trb = priv_ep->interval; >- else >- num_trb = sg_supported ? request->num_mapped_sgs : 1; >+ num_trb = sg_supported ? request->num_mapped_sgs : 1; > > if (num_trb > priv_ep->free_trbs) { > priv_ep->flags |= EP_RING_FULL; > > >*** Problem 2 *** > >According to doc and my observation, looks like hardware fetch data into FIFO >when get SOF, then transfer data when get IN token. Each SOF will increase >TRB regardless it is ready or not. Yes, but this fetched data will be sent in next ITP. > >When gadget complete equeue ISO data, so SOF will increase TRB regardless if >there are IN token. > > SOF SOF SOF SOF IN SOF .... > TRB0 TRB1 TRB2 TRB3 ... > > >Host may start get data at some time after gadget queue data. > >So TRB0..2 data will be lost. > >If it is audio data, it should be okay. But for uvc, it is jpeg header, so host side >report error. > >I checked dwc gadget driver, which start equeue ISO data only get NYET. > >I check cdns spec, there are ISOERR. But it is never happen. According to >document, ISOERR should issue when IN token and FIFO no data. > Current CDNS3 driver has disabled ISOERR. Did you enable it? >I tried below method > 1. Delay queue TRB, but no ISOERR. > 2. queue a lenght 0 TRB,but no ISOERR > >My question is how to delay queue TRB to ISO IN token really happen to avoid >lost JPEG header. > >Frank > > > > >
