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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Daniel,

Thank you for the patch.

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().

Should you mention rcar-du and omapdrm here ?

> 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=0ba17d70d062b2595e1f061231474800f076c7cb
> 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>
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_crtc.c | 7 ++-----
>  drivers/gpu/drm/arm/malidp_drv.c                 | 1 -
>  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c   | 7 ++-----
>  drivers/gpu/drm/drm_atomic_state_helper.c        | 4 ++++
>  drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c        | 2 --
>  drivers/gpu/drm/omapdrm/omap_crtc.c              | 8 +++++---
>  drivers/gpu/drm/omapdrm/omap_drv.c               | 4 ----
>  drivers/gpu/drm/rcar-du/rcar_du_crtc.c           | 6 +-----
>  drivers/gpu/drm/tegra/dc.c                       | 1 -
>  drivers/gpu/drm/tidss/tidss_crtc.c               | 3 +--
>  drivers/gpu/drm/tidss/tidss_kms.c                | 4 ----
>  11 files changed, 15 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> index 56bd938961ee..f33418d6e1a0 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> @@ -492,10 +492,8 @@ static void komeda_crtc_reset(struct drm_crtc *crtc)
>  	crtc->state = NULL;
>  
>  	state = kzalloc(sizeof(*state), GFP_KERNEL);
> -	if (state) {
> -		crtc->state = &state->base;
> -		crtc->state->crtc = crtc;
> -	}
> +	if (state)
> +		__drm_atomic_helper_crtc_reset(crtc, &state->base);
>  }
>  
>  static struct drm_crtc_state *
> @@ -616,7 +614,6 @@ static int komeda_crtc_add(struct komeda_kms_dev *kms,
>  		return err;
>  
>  	drm_crtc_helper_add(crtc, &komeda_crtc_helper_funcs);
> -	drm_crtc_vblank_reset(crtc);
>  
>  	crtc->port = kcrtc->master->of_output_port;
>  
> diff --git a/drivers/gpu/drm/arm/malidp_drv.c b/drivers/gpu/drm/arm/malidp_drv.c
> index 6feda7cb37a6..c9e1ee84b4e8 100644
> --- a/drivers/gpu/drm/arm/malidp_drv.c
> +++ b/drivers/gpu/drm/arm/malidp_drv.c
> @@ -861,7 +861,6 @@ static int malidp_bind(struct device *dev)
>  	drm->irq_enabled = true;
>  
>  	ret = drm_vblank_init(drm, drm->mode_config.num_crtc);
> -	drm_crtc_vblank_reset(&malidp->crtc);
>  	if (ret < 0) {
>  		DRM_ERROR("failed to initialise vblank\n");
>  		goto vblank_fail;
> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> index 10985134ce0b..ce246b96330b 100644
> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> @@ -411,10 +411,8 @@ static void atmel_hlcdc_crtc_reset(struct drm_crtc *crtc)
>  	}
>  
>  	state = kzalloc(sizeof(*state), GFP_KERNEL);
> -	if (state) {
> -		crtc->state = &state->base;
> -		crtc->state->crtc = crtc;
> -	}
> +	if (state)
> +		__drm_atomic_helper_crtc_reset(crtc, &state->base);
>  }
>  
>  static struct drm_crtc_state *
> @@ -528,7 +526,6 @@ int atmel_hlcdc_crtc_create(struct drm_device *dev)
>  	}
>  
>  	drm_crtc_helper_add(&crtc->base, &lcdc_crtc_helper_funcs);
> -	drm_crtc_vblank_reset(&crtc->base);
>  
>  	drm_mode_crtc_set_gamma_size(&crtc->base, ATMEL_HLCDC_CLUT_SIZE);
>  	drm_crtc_enable_color_mgmt(&crtc->base, 0, false,
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index 8fce6a115dfe..9ad74045158e 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -32,6 +32,7 @@
>  #include <drm/drm_device.h>
>  #include <drm/drm_plane.h>
>  #include <drm/drm_print.h>
> +#include <drm/drm_vblank.h>
>  #include <drm/drm_writeback.h>
>  
>  #include <linux/slab.h>
> @@ -93,6 +94,9 @@ __drm_atomic_helper_crtc_reset(struct drm_crtc *crtc,
>  	if (crtc_state)
>  		__drm_atomic_helper_crtc_state_reset(crtc_state, crtc);
>  
> +	if (drm_dev_has_vblank(crtc->dev))
> +		drm_crtc_vblank_reset(crtc);
> +
>  	crtc->state = crtc_state;
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_crtc_reset);
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> index e152016a6a7d..c39dad151bb6 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> @@ -1117,8 +1117,6 @@ static void mdp5_crtc_reset(struct drm_crtc *crtc)
>  		mdp5_crtc_destroy_state(crtc, crtc->state);
>  
>  	__drm_atomic_helper_crtc_reset(crtc, &mdp5_cstate->base);
> -
> -	drm_crtc_vblank_reset(crtc);
>  }
>  
>  static const struct drm_crtc_funcs mdp5_crtc_funcs = {
> 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 *
> diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
> index 242d28281784..4526967978b7 100644
> --- a/drivers/gpu/drm/omapdrm/omap_drv.c
> +++ b/drivers/gpu/drm/omapdrm/omap_drv.c
> @@ -595,7 +595,6 @@ static int omapdrm_init(struct omap_drm_private *priv, struct device *dev)
>  {
>  	const struct soc_device_attribute *soc;
>  	struct drm_device *ddev;
> -	unsigned int i;
>  	int ret;
>  
>  	DBG("%s", dev_name(dev));
> @@ -642,9 +641,6 @@ static int omapdrm_init(struct omap_drm_private *priv, struct device *dev)
>  		goto err_cleanup_modeset;
>  	}
>  
> -	for (i = 0; i < priv->num_pipes; i++)
> -		drm_crtc_vblank_off(priv->pipes[i].crtc);
> -
>  	omap_fbdev_init(ddev);
>  
>  	drm_kms_helper_poll_init(ddev);
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
> index d73e88ddecd0..fe86a3e67757 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
> @@ -975,8 +975,7 @@ static void rcar_du_crtc_reset(struct drm_crtc *crtc)
>  	state->crc.source = VSP1_DU_CRC_NONE;
>  	state->crc.index = 0;
>  
> -	crtc->state = &state->state;
> -	crtc->state->crtc = crtc;
> +	__drm_atomic_helper_crtc_reset(crtc, &state->state);
>  }
>  
>  static int rcar_du_crtc_enable_vblank(struct drm_crtc *crtc)
> @@ -1271,9 +1270,6 @@ int rcar_du_crtc_create(struct rcar_du_group *rgrp, unsigned int swindex,
>  
>  	drm_crtc_helper_add(crtc, &crtc_helper_funcs);
>  
> -	/* Start with vertical blanking interrupt reporting disabled. */
> -	drm_crtc_vblank_off(crtc);
> -

Could this cause an issue, as the interrupt handler can now be
registered with the interrupt left enabled in the hardware after a
reboot, while drm_crtc_vblank_off() would disable it ? It's something
that should likely be handled elsewhere in the driver, with all
interrupts disabled explicitly early in probe, and I don't think the
driver handles enabled interrupts very well today, so it's not a blocker
for me:

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

I would however appreciate your thoughts on this topic, to know if my
understanding is correct (and if this issue could affect other drivers).

>  	/* Register the interrupt handler. */
>  	if (rcar_du_has(rcdu, RCAR_DU_FEATURE_CRTC_IRQ_CLOCK)) {
>  		/* The IRQ's are associated with the CRTC (sw)index. */
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index 83f31c6e891c..9b308b572eac 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -1168,7 +1168,6 @@ static void tegra_crtc_reset(struct drm_crtc *crtc)
>  		tegra_crtc_atomic_destroy_state(crtc, crtc->state);
>  
>  	__drm_atomic_helper_crtc_reset(crtc, &state->base);
> -	drm_crtc_vblank_reset(crtc);
>  }
>  
>  static struct drm_crtc_state *
> diff --git a/drivers/gpu/drm/tidss/tidss_crtc.c b/drivers/gpu/drm/tidss/tidss_crtc.c
> index 89a226912de8..4d01c4af61cd 100644
> --- a/drivers/gpu/drm/tidss/tidss_crtc.c
> +++ b/drivers/gpu/drm/tidss/tidss_crtc.c
> @@ -352,8 +352,7 @@ static void tidss_crtc_reset(struct drm_crtc *crtc)
>  		return;
>  	}
>  
> -	crtc->state = &tcrtc->base;
> -	crtc->state->crtc = crtc;
> +	__drm_atomic_helper_crtc_reset(crtc, &tcrtc->base);
>  }
>  
>  static struct drm_crtc_state *tidss_crtc_duplicate_state(struct drm_crtc *crtc)
> diff --git a/drivers/gpu/drm/tidss/tidss_kms.c b/drivers/gpu/drm/tidss/tidss_kms.c
> index 4b99e9fa84a5..e6ab59eed259 100644
> --- a/drivers/gpu/drm/tidss/tidss_kms.c
> +++ b/drivers/gpu/drm/tidss/tidss_kms.c
> @@ -278,10 +278,6 @@ int tidss_modeset_init(struct tidss_device *tidss)
>  	if (ret)
>  		return ret;
>  
> -	/* Start with vertical blanking interrupt reporting disabled. */
> -	for (i = 0; i < tidss->num_crtcs; ++i)
> -		drm_crtc_vblank_reset(tidss->crtcs[i]);
> -
>  	drm_mode_config_reset(ddev);
>  
>  	dev_dbg(tidss->dev, "%s done\n", __func__);

-- 
Regards,

Laurent Pinchart
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