drm/vc4: crtc: Copy assigned channel to the CRTC

Accessing the crtc->state pointer from outside the modesetting context
is not allowed. We thus need to copy whatever we need from the KMS state
to our structure in order to access it.

In VC4, a number of users of that pointers have crept in over the years,
and the previous commits removed them all but the HVS channel a CRTC has
been assigned.

Let's move this channel in struct vc4_crtc at atomic_begin() time, drop
it from our private state structure, and remove our use of crtc->state
from our vblank handler entirely.

Link: https://lore.kernel.org/all/YWgteNaNeaS9uWDe@phenom.ffwll.local/
Link: https://lore.kernel.org/r/20211025141113.702757-4-maxime@cerno.tech
Fixes: 87ebcd42fb ("drm/vc4: crtc: Assign output to channel automatically")
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_txp.c

@@ -435,6 +435,7 @@ static void vc4_txp_atomic_disable(struct drm_crtc *crtc,
 
 static const struct drm_crtc_helper_funcs vc4_txp_crtc_helper_funcs = {
 	.atomic_check	= vc4_txp_atomic_check,
+	.atomic_begin	= vc4_hvs_atomic_begin,
 	.atomic_flush	= vc4_hvs_atomic_flush,
 	.atomic_enable	= vc4_txp_atomic_enable,
 	.atomic_disable	= vc4_txp_atomic_disable,