On Thu June 7 2012 02:52:06 Laurent Pinchart wrote: > Hi Hans, > > On Wednesday 06 June 2012 10:17:03 Hans Verkuil wrote: > > On Wed 6 June 2012 05:46:34 Laurent Pinchart wrote: > > > On Monday 04 June 2012 12:34:23 Rebecca Schultz Zavin wrote: > > > > I have a system where the data is planar, but the kernel drivers > > > > expect to get one allocation with offsets for the planes. I can't > > > > figure out how to do that with the current dma_buf implementation. I > > > > thought I could pass the same dma_buf several times and use the > > > > data_offset field of the v4l2_plane struct but it looks like that's > > > > only for output. Am I missing something? Is this supported? > > > > > > data_offset is indeed for video output only at the moment, and doesn't > > > seem to be used by any driver in mainline for now. > > > > Actually, data_offset may be set by capture drivers. For output buffers it > > is set by userspace, for capture buffers it is set by the driver. This > > data_offset typically contains meta data. > > Is that documented somewhere ? I wasn't aware of this use case. It is documented in the proposal that Pawel sent, but very poorly if at all in the spec. That needs to be improved. > > > I can't really see a reason why data_offset couldn't be used for video > > > capture devices as well. > > > > > > Sanity checks are currently missing. For output devices we should check > > > that data_offset + bytesused < length in the vb2 core. For input devices > > > the check will have to be performed by drivers. Taking data_offset into > > > account automatically would also be useful. I think most of that should > > > be possible to implement in the allocators. > > > > See this proposal of how to solve this: > > > > http://www.spinics.net/lists/linux-media/msg40376.html > > This requires more discussions regarding how the app_offset and data_offset > fields should be used for the different memory types we support. > > For instance app_offset would not make that much sense for the USERPTR memory > type, as we can include the offset in the user pointer already (using > app_offset there would only make the code more complex without any added > benefit). > > For the MMAP memory type adding an app_offset would require allocating buffers > large enough to accomodate the offset, and would thus only be useful with > CREATE_BUFS. I'm also wondering whether the main use case (passing the buffer > to another device that requires that app_offset) wouldn't be better addressed > by the DMABUF memory type anyway. I'm not going to pursue this unless Google indicates that they need this. And actually I would suggest that they ask Pawel to work on this, after all he made the proposal AND he works for Google :-) Regards, Hans -- 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
