Hi Laurent, Thanks for the patchset! On Thu, May 12, 2016 at 03:18:01AM +0300, Laurent Pinchart wrote: > The metadata video device is used to transfer metadata between > userspace and kernelspace. It supports the metadata buffer type only. I remember we briefly discussed this before but I have to bring this up again: do you think we need a different device node type? It depends purely on the use case for which purpose a DMA engine is used for. The receiver hardware doesn't even really know whether the data is image data or metadata; the hardware may well simply write all of it to memory and that's it. Should we use a different device node type for metadata, every driver which uses sensors connected over the CSI-2 bus --- that hardware is designed to receive metadata using a separate data type which is part of the same stream --- would be required to create one node for image data and another for metadata, essentially doubling the number of data device nodes. Doubling doesn't necessarily sound bad, but modern devices tend to have tens of DMA engines already. For what it's worth, multi-plane buffers use video devices as well so this is not the first time a type of a device node would make use of multiple buffer types. -- Regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx
