Hi, The documentation of drm_atomic_helper_check_modeset() says:
"Drivers which update ->mode_changed (e.g. in their ->atomic_check hooks if a plane update can't be done without a full modeset) _must_ call this function afterwards after that change. It is permitted to call this function multiple times for the same update, e.g. when the ->atomic_check functions depend upon the adjusted dotclock for fifo space allocation and watermark computation."
Then drm_crtc_helper_funcs mode_fixup() callback documentations says:
"Atomic drivers which need to inspect and adjust more state should instead use the @atomic_check callback."
Now an atomic driver that needs to do the both in the check phase: update ->mode_changed and inspect and adjust the mode, is in trouble. This is because any adjusted_mode modifications are reset by the afterwards call of drm_atomic_helper_check_modeset().
I can get the atomic tilcdc driver working either: by using the crtc_helper mode_fixup() calback, tuning the mode once more in mode_set_nofb(), or calling drm_atomic_helper_check_modeset() last in drm_mode_config_funcs atomic_check() callback.
What is the right thing to do? Any of these three approaches (and possibly updating the documentation), or some other option that I did not think of?
Best regards, Jyri