On 03/12/2015 08:37 PM, Florian Echtler wrote: > Hello Hans, > > On 09.03.2015 15:02, Hans Verkuil wrote: >> On 03/09/2015 02:45 PM, Florian Echtler wrote: >>> On 09.03.2015 11:09, Hans Verkuil wrote: >>>> The error almost certainly comes from usb_submit_urb(). That function does some >>>> checks on the sgl: >>>> >>>> I wonder it the code gets there. Perhaps a printk just before the return -EINVAL >>>> might help here (also print the 'max' value). >>>> >>>> So you will have to debug a bit here, trying to figure out which test in the usb >>>> code causes the usb_sg_wait error. >>> I'll do my best to track this down. Do you think this is an error in my >>> code, one in the USB subsystem, or some combination of both? >> >> If the USB core indeed requires scatter-gather segments of specific lengths >> (modulo max), then that explains the problems. >> So as suggested try to see if the usb core bails out in that check and what the >> 'max' value is. It looks like only XHCI allows SG segments of any size, so I really >> suspect that's the problem. But I also need to know the 'max' value to fully >> understand the implications. > Finally managed to confirm your suspicions on a kernel with a patched > dev_err call at the location you mentioned: > > Mar 12 20:33:51 sur40 kernel: [ 1159.509580] (null): urb 0 length > mismatch: length 4080, max 512 > Mar 12 20:33:51 sur40 kernel: [ 1159.509592] sur40 2-1:1.0: error -22 in > usb_sg_wait > > So the SG segments are expected in multiples of 512 bytes. I assume this > is not something I can fix from within my driver? No, you can't. I would use dma-sg, but disable the USERPTR support. Also comment why USERPTR support is disabled. This was interesting :-) Regards, Hans -- 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
