Hi Pavel, On 11/24/2021 11:39 AM, Pavel Hofman wrote: > Hi Minas at all, > > Please does dwc2 (specifically in BCM2835/RPi) support HS ISOC multiple > transactions mc > 1 reliably? I found this condition > https://urldefense.com/v3/__https://elixir.bootlin.com/linux/v5.16-rc2/source/drivers/usb/dwc2/gadget.c*L4041__;Iw!!A4F2R9G_pg!MMNE6CYvWEFeWt8W9pImwNA-N4_04U8UsBWQmu9O9Bwq1HalCAupyb9kzGBAOOMlKmt6xefz$ > > /* High bandwidth ISOC OUT in DDMA not supported */ > if (using_desc_dma(hsotg) && ep_type == USB_ENDPOINT_XFER_ISOC && > !dir_in && mc > 1) { > dev_err(hsotg->dev, > "%s: ISOC OUT, DDMA: HB not supported!\n", __func__); > return -EINVAL; > } > > But I do not know how the Descriptor DMA is critical and whether > disabling it will affect gadget performance seriously. > > I know about the RX FIFO sizing requirement (and TX FIFO too I guess), > the current default values can be increased for that particular use case > if needed. > > I am trying to learn if it made sense to spend time on adding support > for high-bandwidth to the UAC2 audio gadget to allow using larger > bInterval and mc=2,3 at high samplerates/channel counts (sort of "burst > mode" similar to UAC3). When doing some CPU-demanding DSP it would help > to avoid the time-critical handling every 125us microframe. Both OUT and > IN are important. > According programming guide: "Isochronous OUT Transfers The application programming for isochronous out transfers is in the same manner as Bulk OUT transfer sequence, except that the application creates only 1 packet per descriptor for an isochronous OUT endpoint. The controller handles isochronous OUT transfers internally in the same way it handles Bulk OUT transfers, and as depicted in Figure 10-28. If the transfers are for a high-bandwidth endpoint (more than one MPS per μframe ), create as many descriptors as the number of packets in a μframe (number of descriptors = number of packets per μframe). Maximum number of descriptors per μframe per endpoint is three." To program descriptors to start HB ISOC OUT there are no any problem. Problem occurs on completions. If, for example mc > 1, driver will allocate and program mc * (request count) descriptors. If host send mc packets per frame then every mc descriptor perform request completion is not big problem. But if host will send less than mc packets in frame then not clear how to exclude unused descriptors from desc chain which already fetched by core - by stop transfers (disable EP) and re-start transfers (fill again desc chain) from next frame? Or purge unused descs and shifting descriptors "up" in a chain? You can try to implement. Thanks, Minas > > Thanks a lot for your expert advice. > > > Best regards, > > > Pavel. > >
