[Intel-gfx] [PATCH] drm/atomic-helper: reset vblank on crtc reset

Daniel Vetter daniel.vetter at ffwll.ch
Wed May 27 09:53:32 UTC 2020

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.

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
Signed-off-by: Daniel Vetter <daniel.vetter at 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/tegra/dc.c                       | 1 -
 drivers/gpu/drm/tidss/tidss_crtc.c               | 3 +--
 drivers/gpu/drm/tidss/tidss_kms.c                | 4 ----
 8 files changed, 9 insertions(+), 20 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 c2507b7d8512..02904392e370 100644
--- a/drivers/gpu/drm/arm/malidp_drv.c
+++ b/drivers/gpu/drm/arm/malidp_drv.c
@@ -870,7 +870,6 @@ 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;
diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
index ca3368c828d0..9606185c284b 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/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)
-	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]);
 	dev_dbg(tidss->dev, "%s done\n", __func__);

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