On ATI Radeon documentation

10.04.2010 17:12

Two years ago AMD released documentation for Radeon graphics cards from ATI. And everyone was happy and said how this would finally bring good, open source drivers for that hardware.

When I was buying a new desktop computer a month ago that was the deciding factor on my choice of the graphic card. I was tired of complete lack of run-time configuration support (XRandr, etc.) and really bad compositing performance of binary Nvidia drivers. And Intel graphics, which works like a charm on my EeePC, turned out to be nearly impossible to get for a desktop computer. So I went with the cheapest, oldest ATI card I could get - a fan-less Radeon HD 4350 - thinking that that would have the best chance of working properly on Linux.

To be honest, it does work relatively well with the latest radeonhd driver from the git repository. There is some screen flicker when moving windows and scrolling in the browser, but nothing I couldn't live with. Even 3D acceleration is working (Ok, kind-of. Some xscreensaver modules have the habit of Oops-ing the kernel)

A bigger problem turned out to be non-working HDMI audio (I want to also use this computer for watching movies on the TV). So I thought, hardware documentation is out there, driver source is available, I can fix this. No problem, right?

Well, not really. First, the docs released by AMD aren't as good as all those news articles led you to believe. I couldn't find any reference to the registers controlling HDMI audio in there and the driver code is full of comments warning about how the function of this and that register was reverse engineered. For instance support for audio on RV710 and RV730 was only possible once it was discovered that a previously unknown register had to be set.

In the end I did in fact find the cause of the problem and made a workaround in the code (see bug #27575), but the bad feeling that I would probably be better off with some other graphics card remained.

Posted by Tomaž | Categories: Code


Did you try the -ati driver?

Posted by Johan

The ati driver as far as I know just loads radeon or radeonhd driver depending on which card you have.

Right now I'm using the radeon driver with kernel mode switching in 2.6.34 kernel. It has the same HDMI audio problem, but is more stable when switching displays at runtime with xrandr and Firefox scrolling doesn't cause screen flicker.

Posted by Tomaž

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