AMD Radeon RX 480 On Linux
AMD has provided launch-day support for the Radeon RX 480 on Linux in the form of the fully open-source driver stack and the hybrid driver stack.
All Open
This is the first major launch of a graphics card for a completely new generation of hardware where AMD/RTG has been able to provide pre-launch open-source driver support! For weeks now there's been experimental support for Polaris appearing on mailing lists and Git repositories for the various Linux driver components. It was terrific to see this happen and is similar to Intel with their providing of open-source driver support ahead of product launch. Unfortunately, it wasn't quite so smooth nor was it pushed out far enough in advance where any Linux distributions are currently providing the support out-of-the-box.
I previously outlined the requirements for RX 480 Linux support. Currently you need to use a AMDGPU DRM-Fixes branch of the Linux 4.7 kernel as all of the Polaris fixes haven't yet been mainlined to Linux 4.7 (Linux 4.7 is going to be the first kernel release with Polaris support), Mesa Git (fixes are being back-ported to Mesa 12.0), Polaris firmware binaries from Alex Deucher's website until they appear in linux-firmware.git as the ones there are currently out of date, and to be using Git of xf86-video-amdgpu/libdrm. Rolling-release Linux distributions will get these various changes in the weeks ahead while for distributions like Ubuntu it won't be until Ubuntu 16.10 or Fedora 25 later in the year that there will be this support out-of-the-box.
The current open-source driver support for Polaris is basically on-par with what's found for previous GCN GPUs on the AMDGPU kernel driver. There is OpenGL 4.3 support via RadeonSI Gallium3D, the basic compute support via OpenCL 1.1 with Clover, VDPAU / VCE, and PowerPlay. With the Linux 4.8 kernel is when the OverDrive re-clocking support is expected to land. There still hasn't been any communication from AMD when they may be able to open-source their Vulkan driver.
Once getting all of the necessary open-source driver components, everything has been working fine on my end with the Radeon RX 480. I haven't experienced any crashes, re-clocking failures, or any other major Linux driver issues. Albeit it won't be easy for novice/casual Linux users to easily get their system in a suitable state for open-source Polaris support right now, but once all of the code is mainlined and in released form picked up by the various distributions, you should be off to the races.
AMDGPU-PRO
AMD should be releasing an updated AMDGPU-PRO hybrid driver today that supports the Radeon RX 480. The AMDGPU-PRO driver I've been testing the past few days is marked version 16.30.3. This driver provides complete support for the RX 480 with OpenGL 4.5, Vulkan 1.0, and OpenCL 2.0. All of my initial RX 480 testing was done on Ubuntu 16.04 LTS and it worked fine there: this AMDGPU-PRO driver is still distributed as a set of Debian packages and outside of the Polaris changes there isn't any other major alterations to report on with this hybrid driver.
If you want Vulkan support today, better support/performance in select games that don't yet run nicely with RadeonSI Gallium3D, easy OpenCL 2.0, or want to avoid any headaches with getting the Polaris open-source driver support squared away, you'll want to initially stick to using the AMDGPU-PRO driver.
Today's Radeon RX 480 launch has undoubtedly been the best yet for AMD/ATI from an open-source perspective... There's actually code available at launch time that works and with full capabilities of the hardware (no missing PowerPlay/re-clocking, OpenGL support is in good shape, etc) for this major new generation of GPUs (in the past they've had open-source support at launch time just for minor GPU revisions). It's also great that the complementary AMDGPU-PRO driver is also prepped for launch day, but we've seen same-day Linux binary support there generally speaking going back to the Radeon HD 4000 days.
Let's see how these Linux drivers allow the Radeon RX 480 to perform under Linux!