Hi Thomas, On Monday 27 January 2014 09:54:58 Thomas Pugliese wrote: > On Mon, 27 Jan 2014, Laurent Pinchart wrote: > > On Friday 24 January 2014 15:17:28 Thomas Pugliese wrote: > > > Isochronous endpoints on devices with speed == USB_SPEED_WIRELESS can > > > have a max packet size ranging from 1-3584 bytes. Add a case to > > > uvc_endpoint_max_bpi to handle USB_SPEED_WIRELESS. Otherwise endpoints > > > for those devices will fall to the default case which masks off any > > > values > 2047. This causes uvc_init_video to underestimate the > > > bandwidth available and fail to find a suitable alt setting for high > > > bandwidth video streams. > > > > I'm not too familiar with wireless USB, but shouldn't the value be > > multiplied by bMaxBurst from the endpoint companion descriptor ? > > Superspeed devices provide the multiplied value in their endpoint > > companion descriptor's wBytesPerInterval field, but there's no such field > > for wireless devices. > > For wireless USB isochronous endpoints, the values in the endpoint > descriptor are the logical interval and max packet size that the endpoint > can support. They are provided for backwards compatibility for just this > type of situation. You are correct that the actual endpoint > characteristics are the bMaxBurst, wOverTheAirPacketSize, and > bOverTheAirInterval values from the WUSB endpoint companion descriptor but > only the host controller really needs to know about those details. In > fact, the values from the endpoint companion descriptor might actually > over-estimate the bandwidth available since the device can set bMaxBurst > to a higher value than necessary to allow for retries. OK, I'll trust you on that :-) I've taken the patch in my tree and will send a pull request for v3.15. > > Out of curiosity, which device have you tested this with ? > > The device is a standard wired UVC webcam: Quanta CQEC2B (VID: 0x0408, > PID: 0x9005). It is connected to an Alereon Wireless USB bridge dev kit > which allows it to operate as a WUSB device. > > Thomas > > > > Signed-off-by: Thomas Pugliese <thomas.pugliese@xxxxxxxxx> > > > --- > > > > > > drivers/media/usb/uvc/uvc_video.c | 3 +++ > > > 1 file changed, 3 insertions(+) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
