2018-09-17 16:51 GMT+02:00 Hans Verkuil <hverkuil@xxxxxxxxx>: > On 09/11/2018 05:09 PM, Maxime Jourdan wrote: >> - Moved the single instance check (returning -EBUSY) to start/stop streaming >> The check was previously in queue_setup but there was no great location to >> clear it except for .close(). > > Actually, you can clear it by called VIDIOC_REQBUFS with count set to 0. That > freed all buffers and clears this. > > Now, the difference between queue_setup and start/stop streaming is that if you > do this in queue_setup you'll know early on that the device is busy. It is > reasonable to assume that you only allocate buffers when you also want to start > streaming, so that it a good place to know this quickly. > > Whereas with start_streaming you won't know until you call STREAMON, or even later > if you start streaming with no buffers queued, since start_streaming won't > be called until you have at least 'min_buffers_needed' buffers queued (1 for this > driver). So in that case EBUSY won't be returned until the first VIDIOC_QBUF. > > My preference is to check this in queue_setup, but it is up to you to decide. > Just be aware of the difference between the two options. > > Regards, > > Hans I could for instance keep track of which queue(s) have been called with queue_setup, catch calls to VIDIOC_REQBUFS with count set to 0, and clear the current session once both queues have been reset ? You leverage another issue with min_buffers_needed. It's indeed set to 1 but this value is wrong for the CAPTURE queue. The problem is that this value changes depending on the codec and the amount of CAPTURE buffers requested by userspace. Ultimately I want it set to the total amount of CAPTURE buffers, because the hardware needs the full buffer list before starting a decode job. Am I free to change this queue parameter later, or is m2m_queue_init the only place to do it ? Thanks, Maxime
