Hi Florian, On 12/15/2014 04:47 PM, Florian Echtler wrote: > Hi everyone, > > I'm currently working on adding raw sensor video support for the Samsung > SUR40 touchscreen. I've finally found some useful documentation about > videobuf2, and added the required functions to the driver (without > actually delivering data so far, I just wanted to try and stream empty > frames for starters). > > However, I'm running into an issue I have a hard time understanding. In > particular, as soon as I load the kernel module, I'm getting a kernel > oops (NULL pointer dereference) in line 354 or 355 of the attached > source code. The reason is probably that the previous check (in line > 350) doesn't abort - even though I didn't actually provide a buffer, so > the list_head should be empty. As no user space program has actually > opened the video device yet, there shouldn't be any buffers queued, > right? (AFAICT the list is initialized properly in line 490). > > I'd be quite grateful if somebody with more experience can look over the > code and tell me what mistakes I made :-) Why on earth is sur40_poll doing anything with video buffers? That's all handled by vb2. As far as I can tell you can just delete everything from '// deal with video data here' until the end of the poll function. The probably cause of the crash here is that the input device node is created before the 'INIT_LIST_HEAD(&sur40->buf_list);' call, and since udevd (I think) opens new devices immediately after they are created it is likely that sur40_poll is called before buf_list is initialized. But, as I said, that code doesn't belong there at all, so just remove it. Regards, Hans > > Thanks & best regards, Florian > > P.S. The SUR40 is a quite peculiar touchscreen device which does > on-board image processing to provide touch data, but also allows to > retrieve the raw video image. Unfortunately, it's a single USB device > with two endpoints for the different data types, so everything (input & > video) needs to be squeezed into one driver. > -- 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
