So I've been experimenting with support for Dave Airlie's new RandR 1.4 provider object interface, so that Optimus-based laptops can use our driver to drive the discrete GPU and display on the integrated GPU. The good news is that I've got a proof of concept working. During a review of the current code, we came up with a few concerns: 1. The output source is responsible for allocating the shared memory Right now, the X server calls CreatePixmap on the output source screen and then expects the output sink screen to be able to display from whatever memory the source allocates. Right now, the source has no mechanism for asking the sink what its requirements are for the surface. I'm using our own internal pitch alignment requirements and that seems to be good enough for the Intel device to scan out, but that could be pure luck. Does it make sense to add a mechanism for drivers to negotiate this with each other, or is it sufficient to just define a lowest common denominator format and if your hardware can't deal with that format, you just don't get to share buffers? One of my coworkers brought to my attention the fact that Tegra requires a specific pitch alignment, and cannot accommodate larger pitches. If other SoC designs have similar restrictions, we might need to add a handshake mechanism. 2. There's no fallback mechanism if sharing can't be negotiated If RandR fails to share a pixmap with the output sink screen, the whole modeset fails. This means you'll end up not seeing anything on the screen and you'll probably think your computer locked up. Should there be some sort of software copy fallback to ensure that something at least shows up on the display? 3. How should the memory be allocated? In the prototype I threw together, I'm allocating the shared memory using shm_open and then exporting that as a dma-buf file descriptor using an ioctl I added to the kernel, and then importing that memory back into our driver through dma_buf_attach & dma_buf_map_attachment. Does it make sense for user-space programs to be able to export shmfs files like that? Should that interface go in DRM / GEM / PRIME instead? Something else? I'm pretty unfamiliar with this kernel code so any suggestions would be appreciated. -- Aaron P.S. for those unfamiliar with PRIME: Dave Airlie added new support to the X Resize and Rotate extension version 1.4 to support offloading display and rendering to different drivers. PRIME is the DRM implementation in the kernel, layered on top of DMA-BUF, that implements the actual sharing of buffers between drivers. http://cgit.freedesktop.org/xorg/proto/randrproto/tree/randrproto.txt?id=randrproto-1.4.0#n122 http://airlied.livejournal.com/75555.html - update on hotplug server http://airlied.livejournal.com/76078.html - randr 1.5 demo videos ----------------------------------------------------------------------------------- This email message is for the sole use of the intended recipient(s) and may contain confidential information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. ----------------------------------------------------------------------------------- _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
