[PATCH 1/8] drm/atomic-helper: reset vblank on crtc reset

[Maxime Ripard]

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 at ideasonboard.com>
> Reviewed-by: Boris Brezillon <boris.brezillon at collabora.com>
> Acked-by: Liviu Dudau <liviu.dudau at arm.com>
> Acked-by: Thierry Reding <treding at nvidia.com>
> Link: https://syzkaller.appspot.com/bug?id=0ba17d70d062b2595e1f061231474800f076c7cb
> Reported-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> Reported-by: syzbot+0871b14ca2e2fb64f6e3 at syzkaller.appspotmail.com
> Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> Cc: "James (Qian) Wang" <james.qian.wang at arm.com>
> Cc: Liviu Dudau <liviu.dudau at arm.com>
> Cc: Mihail Atanassov <mihail.atanassov at arm.com>
> Cc: Brian Starkey <brian.starkey at arm.com>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: Boris Brezillon <bbrezillon at kernel.org>
> Cc: Nicolas Ferre <nicolas.ferre at microchip.com>
> Cc: Alexandre Belloni <alexandre.belloni at bootlin.com>
> Cc: Ludovic Desroches <ludovic.desroches at microchip.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Thierry Reding <thierry.reding at gmail.com>
> Cc: Jonathan Hunter <jonathanh at nvidia.com>
> Cc: Jyri Sarha <jsarha at ti.com>
> Cc: Tomi Valkeinen <tomi.valkeinen at ti.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Sean Paul <seanpaul at chromium.org>
> Cc: Brian Masney <masneyb at onstation.org>
> Cc: Emil Velikov <emil.velikov at collabora.com>
> Cc: zhengbin <zhengbin13 at huawei.com>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: linux-tegra at vger.kernel.org
> Cc: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-renesas-soc at vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>

Acked-by: Maxime Ripard <mripard at kernel.org>

Maxime