From 427c4a0680a28f87bb9c7bbfeac26b39ef8682ad Mon Sep 17 00:00:00 2001
From: Maxime Ripard <maxime@cerno.tech>
Date: Wed, 23 Sep 2020 10:40:31 +0200
Subject: drm/vc4: crtc: Rework a bit the CRTC state code
Git-commit: 427c4a0680a28f87bb9c7bbfeac26b39ef8682ad
Patch-mainline: v5.10-rc1
References: bsc#1129770

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
cast.

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.

Fixes: 6d6e50039187 ("drm/vc4: Allocate the right amount of space for boot-time CRTC state.")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200923084032.218619-1-maxime@cerno.tech
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/vc4/vc4_crtc.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -997,12 +997,18 @@ static void vc4_crtc_destroy_state(struc
 static 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)
-		crtc->state->crtc = crtc;
+	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 = {