Yep, that's about right, although it's actually GEM on TTM (GEM API is supported, but the GEM API calls are handled using some TTM code).
By the time GEM came out most drivers already *had* TTM implementations. There were some aspects of the proposed GEM API which the devs really liked, and others which didn't seem so broadly useful, so the resolution was to make part of the API driver-specific and standardize the rest.
Most drivers are now implementing the standardized part of the GEM API but building it over their existing TTM code. As a result, it's the GEM API that will be exposed, but if you look inside that GEM code for non-Intel parts you'll find most of TTM. Something like that, anyways.
By the time GEM came out most drivers already *had* TTM implementations. There were some aspects of the proposed GEM API which the devs really liked, and others which didn't seem so broadly useful, so the resolution was to make part of the API driver-specific and standardize the rest.
Most drivers are now implementing the standardized part of the GEM API but building it over their existing TTM code. As a result, it's the GEM API that will be exposed, but if you look inside that GEM code for non-Intel parts you'll find most of TTM. Something like that, anyways.
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