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@ideasonboard.com Reviewed-by: Boris Brezillon boris.brezillon@collabora.com Acked-by: Liviu Dudau liviu.dudau@arm.com Acked-by: Thierry Reding treding@nvidia.com Link: https://syzkaller.appspot.com/bug?id=0ba17d70d062b2595e1f061231474800f076c7c... Reported-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Reported-by: syzbot+0871b14ca2e2fb64f6e3@syzkaller.appspotmail.com Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: "James (Qian) Wang" james.qian.wang@arm.com Cc: Liviu Dudau liviu.dudau@arm.com Cc: Mihail Atanassov mihail.atanassov@arm.com Cc: Brian Starkey brian.starkey@arm.com Cc: Sam Ravnborg sam@ravnborg.org Cc: Boris Brezillon bbrezillon@kernel.org Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch Cc: Thierry Reding thierry.reding@gmail.com Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Jyri Sarha jsarha@ti.com Cc: Tomi Valkeinen tomi.valkeinen@ti.com Cc: Rob Clark robdclark@gmail.com Cc: Sean Paul seanpaul@chromium.org Cc: Brian Masney masneyb@onstation.org Cc: Emil Velikov emil.velikov@collabora.com Cc: zhengbin zhengbin13@huawei.com Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-tegra@vger.kernel.org Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: linux-arm-kernel@lists.infradead.org Cc: linux-renesas-soc@vger.kernel.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com
Acked-by: Maxime Ripard mripard@kernel.org
Maxime