Option 1: as I said, the GPU could have its own, and yes in that case the EK cert would be known to the GPU (or it could have a platform-like cert issued by the GPU OEM).
Option 2: the platform vendor can teach the GPU the EK cert (or the public key for some primary key anyways).
Option 3: the GPU could learn it on first use.
> charitably let's say that's a signed blob that the driver pushes in at startup
That's what TPM vendors do as to the EK cert. Surely if they can do that then so can GPU and platform vendors. Indeed, some platform vendors ship with platform certs.
> but that's still going to be a terrible user experience because you won't get media playback if your machine has a TPM that's too new or .
What do you mean "too new"? Like, you replaced your TPM? That's a thing on servers, but not laptops.
As to "from too niche a vendor", as long as the platform vendor teaches the GPU what the EK cert is, or makes a platform-like cert that the GPU can use to authenticate the TPM, then it's good enough.
Anyways I suspect that MSFT and others don't mind an incrementalist approach. You have a system that can do it their way? Great, it will. You have a system that cannot do it their way? Fine, they'll do weak software DRM for now. There's probably no other way to to get to their dream DRM everywhere state.
