[PATCH v2 1/2] drm/vc4: crtc: Rework a bit the CRTC state code

[Maxime Ripard]

The current CRTC state reset hook in vc4 allocates a vc4_crtc_state
structure as a drm_crtc_state, and relies on the fact that vc4_crtc_state
embeds drm_crtc_state as its first member, and therefore can be safely
casted.

However, this is pretty fragile especially since there's no check for this
in place, and we're going to need to access vc4_crtc_state member at reset
so this looks like a good occasion to make it more robust.

Signed-off-by: Maxime Ripard <maxime at cerno.tech>
Tested-by: Dave Stevenson <dave.stevenson at raspberrypi.com>

---

Changes from v1:
  - new patch
---
 drivers/gpu/drm/vc4/vc4_crtc.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index a393f93390a2..7ef20adedee5 100644
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -852,11 +852,18 @@ void vc4_crtc_destroy_state(struct drm_crtc *crtc,
 
 void vc4_crtc_reset(struct drm_crtc *crtc)
 {
+	struct vc4_crtc_state *vc4_crtc_state;
+
 	if (crtc->state)
 		vc4_crtc_destroy_state(crtc, crtc->state);
-	crtc->state = kzalloc(sizeof(struct vc4_crtc_state), GFP_KERNEL);
-	if (crtc->state)
-		__drm_atomic_helper_crtc_reset(crtc, crtc->state);
+
+	vc4_crtc_state = kzalloc(sizeof(*vc4_crtc_state), GFP_KERNEL);
+	if (!vc4_crtc_state) {
+		crtc->state = NULL;
+		return;
+	}
+
+	__drm_atomic_helper_crtc_reset(crtc, &vc4_crtc_state->base);
 }
 
 static const struct drm_crtc_funcs vc4_crtc_funcs = {
-- 
2.26.2