On Fri, Jun 12, 2020 at 06:00:49PM +0200, Daniel Vetter wrote: > 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(). > > 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. > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> > Acked-by: Liviu Dudau <liviu.dudau@xxxxxxx> > Acked-by: Thierry Reding <treding@xxxxxxxxxx> > Link: https://syzkaller.appspot.com/bug?id=0ba17d70d062b2595e1f061231474800f076c7cb > Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Reported-by: syzbot+0871b14ca2e2fb64f6e3@xxxxxxxxxxxxxxxxxxxxxxxxx > Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Cc: "James (Qian) Wang" <james.qian.wang@xxxxxxx> > Cc: Liviu Dudau <liviu.dudau@xxxxxxx> > Cc: Mihail Atanassov <mihail.atanassov@xxxxxxx> > Cc: Brian Starkey <brian.starkey@xxxxxxx> > Cc: Sam Ravnborg <sam@xxxxxxxxxxxx> > Cc: Boris Brezillon <bbrezillon@xxxxxxxxxx> > Cc: Nicolas Ferre <nicolas.ferre@xxxxxxxxxxxxx> > Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> > Cc: Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx> > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > Cc: Maxime Ripard <mripard@xxxxxxxxxx> > Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> > Cc: David Airlie <airlied@xxxxxxxx> > Cc: Daniel Vetter <daniel@xxxxxxxx> > Cc: Thierry Reding <thierry.reding@xxxxxxxxx> > Cc: Jonathan Hunter <jonathanh@xxxxxxxxxx> > Cc: Jyri Sarha <jsarha@xxxxxx> > Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx> > Cc: Rob Clark <robdclark@xxxxxxxxx> > Cc: Sean Paul <seanpaul@xxxxxxxxxxxx> > Cc: Brian Masney <masneyb@xxxxxxxxxxxxx> > Cc: Emil Velikov <emil.velikov@xxxxxxxxxxxxx> > Cc: zhengbin <zhengbin13@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: linux-tegra@xxxxxxxxxxxxxxx > Cc: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Cc: linux-renesas-soc@xxxxxxxxxxxxxxx > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> Acked-by: Maxime Ripard <mripard@xxxxxxxxxx> Maxime
