From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans Verkuil Subject: Re: [PATCH v3][RFC] add raw video stream support for Samsung SUR40 Date: Sun, 15 Mar 2015 17:26:40 +0100 Message-ID: <5505B2C0.6090309@xs4all.nl> References: <1423063842-6902-1-git-send-email-floe@butterbrot.org> <54DB4295.1080307@butterbrot.org> <54E1D71C.2000003@xs4all.nl> <54E7AB1E.3000401@butterbrot.org> <54E85C48.6070907@xs4all.nl> <54F98E51.8040204@butterbrot.org> <54F993ED.2060701@xs4all.nl> <54FB5715.2090103@butterbrot.org> <54FB6636.6050308@xs4all.nl> <54FD6CAD.9030600@butterbrot.org> <54FD713D.5050401@xs4all.nl> <54FDA3EA.9080006@butterbrot.org> <54FDA7E5.3010004@xs4all.nl> <5501EB0B.5020806@butterbrot.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5501EB0B.5020806@butterbrot.org> Sender: linux-media-owner@vger.kernel.org To: Florian Echtler , Mauro Carvalho Chehab Cc: Laurent Pinchart , linux-input , LMML List-Id: linux-input@vger.kernel.org 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