Hi Florian, On 12/16/14 13:35, Florian Echtler wrote: > On 15.12.2014 23:34, Hans Verkuil wrote: >> On 12/15/2014 11:15 PM, Florian Echtler wrote: >>> On 15.12.2014 17:01, Hans Verkuil wrote: >>>> On 12/15/2014 04:47 PM, Florian Echtler wrote: >>>> 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. >>> Right now, the code doesn't do anything, but I'm planning to add the >>> actual data retrieval at this point later. I'd like to use the >>> input_polldev thread for this, as a) the video data should be fetched >>> synchronously with the input device data and b) the thread will be >>> running continuously anyway. >> Ah, now I see it. > One additional question you might be able to answer: if I use > vb2_dma_contig_init_ctx for the allocator context, will usb_bulk_msg > with a vb2_buffer then automatically use DMA? No, it won't. > I want to avoid > unnecessary memcpy operations, so ideally the USB host controller should > directly put the data into the buffer which is then passed to userspace. > Does this require any additional setup? I don't think you can do that since the USB packets need to be unpacked (header stripped off, etc.), so you need to do a memcpy anyway. I'm no USB expert, but it is my understanding that you always need to memcpy. So it probably makes more sense for you to use videobuf2-vmalloc instead of dma-contig since there is no requirement for physically contiguous memory. All V4L2 USB drivers that I know off all use vb2-vmalloc. Regards, Hans > >>>> But, as I said, that code doesn't belong there at all, so just remove it. >>> See above - that was actually intentional. It's kind of a hackish >>> solution, but for the moment, I'd just like to get a video stream with >>> minimal overhead, so I'm reusing the polldev thread. >> OK. If you are planning to upstream this driver, then this probably needs >> another look. > Once I get it working, I'll submit a patch for further discussion. > > Best, Florian > -- 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
