[PATCH v3] drm/fourcc: document modifier uniqueness requirements

[Daniel Stone]

On Wed, 3 Jun 2020 at 19:53, Marek Olšák <maraeo at gmail.com> wrote:
> TMZ is more complicated. If there is a TMZ buffer used by a command buffer, then all other used buffers must also be TMZ or read only. If no TMZ buffers are used by a command buffer, then TMZ is disabled. If a context is not secure, TMZ is also disabled. A context can switch between secure and non-secure based on the buffers being used.
>
> So mixing secure and non-secure memory writes in one command buffer won't work. This is not fixable in the driver - apps must be aware of this.

Sure, that makes sense. It probably points to TMZ being its own
special thing, independent of modifiers, since it touches so much
global state, and doesn't mesh cleanly any of the models we have for
advertising and negotiating buffer allocation and import.

Cheers,
Daniel