Hi Thomas, On Monday 14 April 2014 21:07:12 Thomas Pugliese wrote: > On Mon, 27 Jan 2014, Laurent Pinchart wrote: > > 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(+) > > So it turns out that this change (commit 79af67e77f86404e77e65ad954bf) > breaks wireless USB devices that were designed to work with Windows > because Windows also does not differentiate between Wireless USB devices > and USB 2.0 high speed devices. This change should probably be reverted > before it goes out in the 3.15 release. Devices that are strictly WUSB > spec compliant will not work with some max packet sizes but they never did > anyway. > > In order to support both compliant and non-compliant WUSB devices, > uvc_endpoint_max_bpi should look at the endpoint companion descriptor but > that descriptor is not readily available as it is for super speed devices > so that patch will have to wait for another time. Could you please send me a proper revert patch with the above description in the commit message and CC Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx> ? -- 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
