On Fri, Mar 1, 2013 at 1:42 AM, John Stultz john.stultz@linaro.org wrote:
As proposed yesterday, here's the Android sync driver patches for staging.
I've preserved the commit history, but moved all the changes over to be against the staging directory (instead of drivers/base).
The goal of submitting this driver to staging is to try to get more collaberation, as there are some similar efforts going on in the community with dmabuf-fences. My email from yesterday with more details for how I hope this goes is here: http://comments.gmane.org/gmane.linux.kernel/1448420
I've been offline in a week of snowboarding, but I'll throw my late Ack - I've discussed this a bit with John offline and I agree with his general plan for integrating android sync points into mainline.
Erik also provided a nice background on the patch set in his reply yesterday, which I'll quote here:
"In Honeycomb where we introduced the Hardware Composer HAL. This is a userspace layer that allows composition acceleration on a per platform basis. Different SoC vendors have implemented this using overlays, 2d blitters, a combinations of both, or other clever/disgusting means. Along with the HWC we consolidated a lot of our camera and media pipeline to allow their input to be fed into the GPU or display(overlay.) In order to exploit parallelism the the graphics pipeline, this introduced lots of implicit synchronization dependancies. After a couple years of working with many different SoC vendors, we found that it was really difficult to communicate our system's expectations of the implicit contract and it was difficult for the SoC vendors to properly implement the implicit contract in each of their IP blocks (display, gpu, camera, video codecs). It was also incredibly difficult to debug when problems/deadlocks arose.
dma_buf fences should be tons easier to debug thanks to integration with lockdep. Also their design fundamentally excludes deadlock-loops in the fences themselves. And I also think that we should be able to hide the complexity from most drivers in e.g. drm/ttm or the v2l core. So I'm still bullish on implicit fencing (and will keep on pushing that for all things intel).
But I guess the simpler programming model afforded by that for userspace isn't of much use for the google guys now that they've pushed the effort to convert SurfaceFlinger to explicit fence handling ...
Cheers, Daniel