Linux 4.7 Adding DP++ Dongle Detection For The Intel DRM Driver

Written by Michael Larabel in Hardware on 27 May 2016 at 10:42 AM EDT. 3 Comments
Following the DRM feature pull for Linux 4.7 sent at the beginning of the week, David Airlie has now sent in a batch of "DRM fixes" for Linux 4.7 that does include some new functionality too.

One of the features to this latest pull request is support in the Intel DRM driver for offering DP++ dongle detection. DP++ / DisplayPort++ is also known as Dual-Mode DisplayPort and it's for directly outputting single-link HDMI/DVI signals using a passive adapter on a DisplayLink source. DP++ is supported by most hardware out there but the Intel driver up to now hasn't detected DP++ adapters, thus making these DP-to-HDMI/DVI dongles not work.

With this pull request comes DP++ dongle detection, which in turn was also used to fix some regressions in the driver's HDMI color depth code. Some of this DisplayPort++ detection code was added as a generic DRM helper that will be able to help other DRM drivers in their dual-mode DisplayPort support.

For those wanting to go from DisplayPort to HDMI or DVI with DP++, there are a range of adapters available via our friends at Most of these adapters will set you back less than $20 USD.

Besides working on this dual-mode DP / DP++ code for the Intel driver there is also fixed HDMI deep color support in the AMDGPU DRM driver and the previously-covered PowerPlay fixes and AMD Polaris ID / golden setting additions. There are also some clocking-related fixes ahead of the AMDGPU OverDrive support that will come in Linux 4.8.

The complete list of changes for this "DRM fixes" pull for 4.7 can be found via the kernel mailing list. The pull adds over 500 lines of new code, in large part due to the new DP dual-mode code.
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