Ah ok, I didn't know that. Thanks for the info - I'll try the option and see
how it goes ;-)

Unrealted to the acceleration I discovered another error message in my dmesg:
[drm:ci_dpm_set_power_state] *ERROR* ci_upload_dpm_level_enable_mask failed
Should I report that in a new bug ? (I should really stop hijacking this bug,
sorry)