drm/atomic-helper: reset vblank on crtc reset

Only when vblanks are supported ofc.

Some drivers do this already, but most unfortunately missed it. This
opens up bugs after driver load, before the crtc is enabled for the
first time. syzbot spotted this when loading vkms as a secondary
output. Given how many drivers are buggy it's best to solve this once
and for all in shared helper code.

Aside from moving the few existing calls to drm_crtc_vblank_reset into
helpers (i915 doesn't use helpers, so keeps its own) I think the
regression risk is minimal: atomic helpers already rely on drivers
calling drm_crtc_vblank_on/off correctly in their hooks when they
support vblanks. And driver that's failing to handle vblanks after
this is missing those calls already, and vblanks could only work by
accident when enabling a CRTC for the first time right after boot.

Big thanks to Tetsuo for helping track down what's going wrong here.

There's only a few drivers which already had the necessary call and
needed some updating:
- komeda, atmel and tidss also needed to be changed to call
  __drm_atomic_helper_crtc_reset() intead of open coding it
- tegra and msm even had it in the same place already, just code
  motion, and malidp already uses __drm_atomic_helper_crtc_reset().
- Laurent noticed that rcar-du and omap open-code their crtc reset and
  hence would actually be broken by this patch now. So fix them up by
  reusing the helpers, which brings the drm_crtc_vblank_reset() back.

Only call left is in i915, which doesn't use drm_mode_config_reset,
but has its own fastboot infrastructure. So that's the only case where
we actually want this in the driver still.

I've also reviewed all other drivers which set up vblank support with
drm_vblank_init. After the previous patch fixing mxsfb all atomic
drivers do call drm_crtc_vblank_on/off as they should, the remaining
drivers are either legacy kms or legacy dri1 drivers, so not affected
by this change to atomic helpers.

v2: Use the drm_dev_has_vblank() helper.

v3: Laurent pointed out that omap and rcar-du used drm_crtc_vblank_off
instead of drm_crtc_vblank_reset. Adjust them too.

v4: Laurent noticed that rcar-du and omap open-code their crtc reset
and hence would actually be broken by this patch now. So fix them up
by reusing the helpers, which brings the drm_crtc_vblank_reset() back.

v5: also mention rcar-du and ompadrm in the proper commit message
above (Laurent).

Reviewed-by: Laurent Pinchart <[email protected]>
Acked-by: Maxime Ripard <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Reviewed-by: Boris Brezillon <[email protected]>
Acked-by: Liviu Dudau <[email protected]>
Acked-by: Thierry Reding <[email protected]>
Link: https://syzkaller.appspot.com/bug?id=0ba17d70d062b2595e1f061231474800f076c7cb
Reported-by: Tetsuo Handa <[email protected]>
Reported-by: [email protected]
Cc: Tetsuo Handa <[email protected]>
Cc: "James (Qian) Wang" <[email protected]>
Cc: Liviu Dudau <[email protected]>
Cc: Mihail Atanassov <[email protected]>
Cc: Brian Starkey <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Boris Brezillon <[email protected]>
Cc: Nicolas Ferre <[email protected]>
Cc: Alexandre Belloni <[email protected]>
Cc: Ludovic Desroches <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: Jonathan Hunter <[email protected]>
Cc: Jyri Sarha <[email protected]>
Cc: Tomi Valkeinen <[email protected]>
Cc: Rob Clark <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: Brian Masney <[email protected]>
Cc: Emil Velikov <[email protected]>
Cc: zhengbin <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: Kieran Bingham <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/gpu/drm/omapdrm/omap_crtc.c b/drivers/gpu/drm/omapdrm/omap_crtc.c
index fce7e944a280..6d40914675da 100644
--- a/drivers/gpu/drm/omapdrm/omap_crtc.c
+++ b/drivers/gpu/drm/omapdrm/omap_crtc.c
@@ -697,14 +697,16 @@ static int omap_crtc_atomic_get_property(struct drm_crtc *crtc,
 
 static void omap_crtc_reset(struct drm_crtc *crtc)
 {
+	struct omap_crtc_state *state;
+
 	if (crtc->state)
 		__drm_atomic_helper_crtc_destroy_state(crtc->state);
 
 	kfree(crtc->state);
-	crtc->state = kzalloc(sizeof(struct omap_crtc_state), GFP_KERNEL);
 
-	if (crtc->state)
-		crtc->state->crtc = crtc;
+	state = kzalloc(sizeof(*state), GFP_KERNEL);
+	if (state)
+		__drm_atomic_helper_crtc_reset(crtc, &state->base);
 }
 
 static struct drm_crtc_state *