Hi I am currently working on fblog [1] (a replacement for fbcon without VT dependencies) but this questions does also apply to other fbdev users. Is there a way to share framebuffers between fbdev devices? I was thinking especially of USB devices like DisplayLink. If they share the same screen dimensions it would increase performance a lot if I could display a single buffer on all the devices instead of copying it into each framebuffer. I was told to have a look at the dma-buf framework to implement this. However, looking at the fbdev dma-buf support I think that this isn't currently possible. Each fbdev device takes the exporter-role and provides a single dma-buf object. However, if I wanted to share the buffers, I would need to be the exporter. Or there needs to be a way for the fbdev devices to import a dma-buf from other fbdev devices. I also took a short look at DRM prime support and noticed that it is capable of importing buffers (or at least it looks like it is). Therefore, I was wondering whether it does make sense to add an "import dma-buf" callback to fbdev devices and if the fbdev driver supports this, I can simply draw to a single dma-buf from one fbdev device and push it to all other fbdev devices that share the same dimensions. It would also be nice to allow multiple buffer-owners or a way to transfer ownership. That is, if the owner/exporter of the dma-buf vanishes, I would pass it to another fbdev device which would pick it up so I don't have to create a new one. I think this is only interesting for DisplayLink-devices as they are currently the only way to get a bunch of displays connected to a single machine. Anyway, if you think that this isn't worth it, I will probably drop this idea. Regards David [1] fblog kernel driver: http://lwn.net/Articles/505965/ -- 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
