At least from coding style, backward compatibility etc.. this looks sane to me, so feel free to add an Acked-by.
But I absolutely can't judge if that is correct from the hardware point of view or not.
Our GDS docs say that writing the register resets the wave counter.
And I think that somebody else looking at this is mandatory for it to be committed.
There won't be anybody else. Nobody here really understands GDS, nobody here really cares about GDS, and hw guys weren't helpful with the hangs. If I didn't discover this by luck, GDS OA would be unusable on Linux.