nvk: blackwell support

Blog posts are like buses sometimes...

I've spent time over the last month enabling Blackwell support on NVK, the Mesa vulkan driver for NVIDIA GPUs. Faith from Collabora, the NVK maintainer has cleaned up and merged all the major pieces of this work and landed them into mesa this week. Mesa 25.2 should ship with a functioning NVK on blackwell. The code currently in mesa main passes all tests in the Vulkan CTS.

Quick summary of the major fun points:

Ben @ NVIDIA had done the initial kernel bringup in to r570 firmware in the nouveau driver. I worked with Ben on solidifying that work and ironing out a bunch of memory leaks and regressions that snuck in.

Once the kernel was stable, there were a number of differences between Ada and Blackwell that needed to be resolved. Thanks to Faith, Mel and Mohamed for their help, and NVIDIA for providing headers and other info.

I did most of the work on a GB203 laptop and a desktop 5080.

1. Instruction encoding: a bunch of instructions changed how they were encoded. Mel helped sort out most of those early on.

2. Compute/QMD: the QMD which is used to launch compute shaders, has a new encoding. NVIDIA released the official QMD headers which made this easier in the end.

3. Texture headers: texture headers were encoded different from Hopper on, so we had to use new NVIDIA headers to encode those properly

4. Depth/Stencil: NVIDIA added support for separate d/s planes and this also has some knock on effects on surface layouts. 

5. Surface layout changes. NVIDIA attaches a memory kind to memory allocations, due to changes in Blackwell, they now use a generic kind for all allocations. You now longer know the internal bpp dependent layout of the surfaces. This means changes to the dma-copy engine to provide that info. This means we have some modifier changes to cook with NVIDIA over the next few weeks at least for 8/16 bpp surfaces. Mohamed helped get this work and host image copy support done.

6. One thing we haven't merged is bound texture support. Currently blackwell is using bindless textures which might be a little slower. Due to changes in the texture instruction encoding, you have to load texture handles to intermediate uniform registers before using them as bound handles. This causes a lot of fun with flow control and when you can spill uniform registers. I've written a few efforts at using bound textures, so we understand how to use them, just have some compiler issues to maybe get it across the line.

7. Proper instruction scheduling isn't landed yet. I have a spreadsheet with all the figures, and I started typing, so will try and get that into an MR before I take some holidays.