On Wed 6 June 2012 05:46:34 Laurent Pinchart wrote:
Hi Rebecca,
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.
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
Regards,
Hans