When the Radeon HD 4850 and Radeon HD 4870 were introduced earlier this year, it was wonderful. These latest high-end graphics cards from ATI had same-day Linux support through their Catalyst driver and the open-source ATI drivers had "just worked" with the RV770 series. The mode-setting support with the xf86-video-ati and xf86-video-radeonhd drivers just required adding in the PCI IDs for these new PCI Express graphics cards and then the rest of the magic was provided by AtomBIOS. However, with the introduction of the Radeon HD 4600 series, not everything is working instantly with the open-source drivers.
The kind folks at Sapphire Technology had sent out the ATI Radeon HD 4670 graphics card upon its release. The Radeon HD 4670 retails well under $100 USD and has 512MB of GDDR3 memory with a 128-bit interface. Its RV730 core operates at 750MHz and the memory is running at 1000MHz. We will have our full review on the Sapphire Radeon HD 4670 in the near future, but for now we just want to share its open-source status.
We were successful in using the Radeon HD 4850 with an open driver and HD 4870 since most of the architectural changes between the R600 and RV770 are hidden behind the AtomBIOS interface. AtomBIOS is the video BIOS abstraction layer that was designed by ATI and has been implemented within their graphics cards since the R400 series. AtomBIOS itself isn't open-source but their parser is available and most recently they had released a new version. The xf86-video-ati driver has been using AtomBIOS since last year when they decided to add support for the R500/600 series, while it wasn't until July when the RadeonHD driver finally and fully adopted AtomBIOS under pressure from AMD.
With there being more changes from the R600 to RV770 compared to the RV770 to RV730, we expected the Radeon HD 4670 too would "just work" with AtomBIOS and the open-source drivers, but this wasn't the case. After adding in the Radeon HD 4670 PCI ID (0x9490) and rebuilding the driver, it hadn't worked when using a DVI display. The RadeonHD driver wasn't able to output a signal but with the ATI driver it had outputted a signal but the screen remained black. Switching though to using a 1280 x 1024 LCD panel with a VGA interface, both drivers had then successfully worked.
The open-source ATI developers have yet to receive the Radeon HD 4650 or Radeon HD 4670 graphics cards, but we have supplied them with a copy of the video BIOS and verbose logs. There are some display controller changes on the RV730 with the output blocks, but in theory, AtomBIOS should have concealed the differences. Ideally, we will see support for the new RV730 digital output blocks in the near future. For those interested in full 3D support, CrossFire, OverDrive, and other advanced features will need to use AMD's Catalyst driver for Linux. Catalyst 8.9 to be released this month will officially support the Radeon HD 4600 series.