Eric Anholt (anholt) wrote,
Eric Anholt

This week in vc4 (2017-01-24): LCA, DSI, HDMI audio

I spent last week at 2017 (the best open source conference), mostly talking to people and going to talks instead of acually hacking on vc4.  I'd like to highlight a few talks you could go watch if you weren't there.

Jack Moffit gave an overview of what Servo is doing with Rust on parallel processing and process isolation in web engines.  I've been hacking on this project in my spare time, and the community is delightful to work with.  Check out his talk to see what I've been excited about recently.

I then spent the next session in the hallway chatting with him instead of going to Willy's excellent talk about how the Linux page cache works.  One of the subjects of that talk makes me wonder: I've got these contiguous regions of GPU memory on VC4, could I use huge pages when we're mapping them for uploads to the GPU?  Would they help enough to matter?

Dave Airlie gave a talk about the structure of the Vulkan drivers and his work with Bas on the Radeon Vulkan driver.  It's awesome how quickly these two have been able to turn around a complete Vulkan driver, and it really validates our open source process and the stack we've built in Mesa.

Nathan Egge from Mozilla gave a talk on accelerating JPEG decode using the GPU.  I thought it was going to be harder to do than he made it out to be, so it was pretty cool to see the performance improvements he got.  The only sad part was that it isn't integrated into WebRender yet as far as I can see.

Karen Sandler talked about the issue of what happens to our copyrights when we die, from experience in working with current project maintainers on relicensing efforts.  I think this is a really important talk for anyone who writes copyleft software.  It actually softened my stance on CLAs (!) but is mostly a call to action for "Nobody has a good process yet for dealing with our copyrights after death, let's work on this."

And, finally, I think the most important talk of the conference to me was Daniel Vetter's Maintainers Don't Scale (no video yet, just a blog post).  The proliferation of boutique trees in the kernel with "overworked" maintainers either ignoring or endlessly bikeshedding the code of outside contributors is why I would never work on the Linux kernel if I wasn't paid to do so.  Daniel actually offers a way forward from the current state of maintainership in the kernel, with group maintainership (a familiar model in healthy large projects) to replace DRM's boutique trees and a reinforcement of the cooperative values that I think are why we all work on free software.  I would love to be able to shut down my boutique DRM and ARM platform trees.

In VC4, I did still manage to write a couple of kernel fixes in response to a security report, and rebase DSI on 4.10 and respin some of its patches for resubmission.  I'm still hoping for DSI in 4.11, but as usual it depends on DT maintainer review (no response for over a month).  I also spent a lot of time with Keith talking about ARM cache coherency questions and trying experiments on my NEON tiling code.

While I was mostly gone last week, though, Boris has been working on finish off my HDMI audio branch.  He now has a branch that has a seriously simplified architecture compared to what I'd talked about with larsc originally (*so* much cleaner than what I was modeling on), and he has it actually playing some staticy audio.  He's now debugging what's causing the static, including comparing dumps of raw audio between VC4 and the firmware, along with the register settings of the HDMI and DMA engines.
Tags: vc4
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