quoted

Under which circumstances would you become interested to apply a statement
like “guard(spinlock_irqsave)(&crtc->dev->event_lock);”?

I just follow the kerneldoc of drm_crtc_send_vblank_event() to
hold event lock like many other drivers do.

Please take another look at software design possibilities to benefit more
from further applications of scope-based resource management.

Regards,
Markus