NVIDIA Releases A Bit More Open GPU Documentation
Written by Michael Larabel in NVIDIA on 25 October 2013 at 04:17 AM EDT. 9 Comments
Last month NVIDIA announced they would begin providing open-source GPU documentation and ultimately supporting the reverse-engineered open-source Nouveau graphics driver project for their Linux desktop customers. NVIDIA released some basic documentation in that initial push and now they have followed up with a tiny bit more documentation.

The new "open NVIDIA documentation" that was made public this week isn't as exciting as AMD's 3D/Compute GPU documentation but the new text file documentation is helpful if you're a GK104 GPU owner and have been having issues with Nouveau.

The new documentation file made public is basically making public an error in the GK104 video BIOS that could cause problems for users of non-official NVIDIA drivers.

It turns out that a diagnostic setting was left enabled in the production vBIOS builds of some GK104-based graphics cards, including the GeForce GTX 680M, GeForce GTX 670MQ, Quadro K4000M, Quadro K4000M, and some other related GPUs. The diagnostic setting left on is where the vBIOS will turn a display output to red in case of display engine under-flows. The display would be red or just red pixels where pixels are missing.

Display engine under-flows is an occurrence where the current GPU performance state limits the GPU video memory bandwidth to an amount lower than the current streaming requirements for the display engine, i.e. the driver aggressively set the memory frequency too low. By making the screen red in debug builds of the video BIOS, it's easy for developers to see this problem is happening.

So NVIDIA's new documentation is just making known this situation and that some video BIOSes may have the setting on. For resolving it, the NVIDIA Linux driver disables the setting and so for helping Nouveau, NVIDIA pointed out the four per-head registers that can be set to avoid this debug feature. At least their documentation properly documented these few registers to address a problem a small number of Nouveau Linux users have encountered. From another perspective, this could potentially be of use to the Nouveau developers in being able to tap this feature for better testing when dealing with their troubled re-clocking support.

Those interested in seeing NVIDIA's open documentation can find it from the NVIDIA.com FTP server.
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Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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