drm/amd/display: defer modeset check in dm_update_planes_state

amdgpu_dm_atomic_check() is used to validate the entire configuration of
planes and crtc's that the user space wants to commit.

However amdgpu_dm_atomic_check() depends upon DRM_MODE_ATOMIC_ALLOW_MODESET
flag else its mostly dummy.
Its not mandatory for the user space to set DRM_MODE_ATOMIC_ALLOW_MODESET,
and in general its not set either along with DRM_MODE_ATOMIC_TEST_ONLY.

Considering its importantance, this patch defers the allow_modeset check
in dm_update_planes_state(), so that there shall be scope to validate
the configuration sent from user space, without impacting the population
of dc/dm related data structures.

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4636,8 +4636,6 @@ static int dm_update_planes_state(struct dc *dc,
 	bool pflip_needed  = !state->allow_modeset;
 	int ret = 0;
 
-	if (pflip_needed)
-		return ret;
 
 	/* Add new planes */
 	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
@@ -4652,6 +4650,8 @@ static int dm_update_planes_state(struct dc *dc,
 
 		/* Remove any changed/removed planes */
 		if (!enable) {
+			if (pflip_needed)
+				continue;
 
 			if (!old_plane_crtc)
 				continue;
@@ -4696,6 +4696,8 @@ static int dm_update_planes_state(struct dc *dc,
 			if (!dm_new_crtc_state->stream)
 				continue;
 
+			if (pflip_needed)
+				continue;
 
 			WARN_ON(dm_new_plane_state->dc_state);