Hello Shuah, On 07/15/2016 03:42 PM, Shuah Khan wrote: > On 07/15/2016 10:26 AM, Javier Martinez Canillas wrote: >> The buffer planes' dma-buf are currently mapped when buffers are queued >> from userspace but it's more appropriate to do the mapping when buffers >> are queued in the driver since that's when the actual DMA operation are >> going to happen. >> >> Suggested-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx> >> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx> >> >> --- >> >> Hello, >> >> A side effect of this change is that if the dmabuf map fails for some >> reasons (i.e: a driver using the DMA contig memory allocator but CMA >> not being enabled), the fail will no longer happen on VIDIOC_QBUF but >> later (i.e: in VIDIOC_STREAMON). >> >> I don't know if that's an issue though but I think is worth mentioning. > > How does this change impact the user applications.? This changes One thing that Nicolas mentioned is that for example GStreamer uses QBUF to detect if a dma-buf is compatible, and fallbacks to a slow path if that's not the case. For example if VIDIOC_QBUF fails, gst can attempt to do another VIDIOC_REQBUFS with a different streaming I/O method as a fallback. If now QBUF doesn't fail, then gst will believe that it's OK and drop the buffer so won't be able to recover from an error later and do a fallback. Now, I don't know if that is the correct thing to expect since the v4l2 doc for VIDIOC_QBUF doesn't say that the ioctl should be used for this. The question is if validating that the exported dma-buf can be imported is something that could be done without attempting to do the mapping. > the behavior and user applications now get dmabuf map error at a > later stage in the call sequence. > > The change itself looks consistent with the change described. > > -- Shuah > Best regards, -- Javier Martinez Canillas Open Source Group Samsung Research America -- 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
