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Message-ID: <Z367rzpzt00F0sK9@phenom.ffwll.local>
Date: Wed, 8 Jan 2025 18:53:51 +0100
From: Simona Vetter <simona.vetter@...ll.ch>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Rob Clark <robdclark@...il.com>,
Abhinav Kumar <quic_abhinavk@...cinc.com>,
Sean Paul <sean@...rly.run>,
Marijn Suijten <marijn.suijten@...ainline.org>,
Chandan Uddaraju <chandanu@...eaurora.org>,
Jeykumar Sankaran <jsanka@...eaurora.org>,
Jordan Crouse <jordan@...micpenguin.net>,
Sravanthi Kollukuduru <skolluku@...eaurora.org>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
Archit Taneja <architt@...eaurora.org>,
Rajesh Yadav <ryadav@...eaurora.org>, linux-arm-msm@...r.kernel.org,
freedreno@...ts.freedesktop.org,
Simona Vetter <simona.vetter@...ll.ch>
Subject: Re: [PATCH 2/6] drm/atomic: prepare to check that drivers follow
restrictions for needs_modeset
On Sun, Dec 22, 2024 at 07:00:42AM +0200, Dmitry Baryshkov wrote:
> Some drivers might fail to follow the restrictions documented for
> drm_atomic_helper_check_modesets(). In order to catch such an issues,
> add the drm_atomic_state->dirty_needs_modeset field and check it in
> drm_atomic_check_only(). Make sure that neither of atomic_check()
> callbacks can set that field without calling
> drm_atomic_helper_check_modesets() again.
>
> Suggested-by: Simona Vetter <simona.vetter@...ll.ch>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Thanks a lot of creating this patch. But looking at it I'm not so sure I
actually had a good idea, since there's still lots of ways for drivers to
change drm_atomic_crtc_needs_modeset() that we miss. And trying to use an
inverted bitfield of all crtc that we've run through in check_modeset, and
then in atomic_check_only compare it against all crtc that need a modeset
also has corner cases it gets wrong I think, like just not using the
helpers in specific case, I think something like i915's fastset would trip
that.
Plus there's lots more corners that drivers have gotten creatively wrong,
so I feel like really clear docs is the best we can do.
So unless you think it was really useful to fix msm I feel like best to
skip this. Apologies for making you put work in here :-/
-Sima
> ---
> drivers/gpu/drm/drm_atomic.c | 3 ++
> drivers/gpu/drm/drm_atomic_helper.c | 77 +++++++++++++++++++++++++++++++++----
> include/drm/drm_atomic.h | 10 +++++
> 3 files changed, 82 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 9ea2611770f43ce7ccba410406d5f2c528aab022..202e4e64bd31921d0a4d4b86605b501311e14c33 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1449,6 +1449,9 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
> }
> }
>
> + WARN_RATELIMIT(state->dirty_needs_modeset,
> + "Driver changed needs_modeset under drm_atomic_helper_check_modeset()");
> +
> if (!state->allow_modeset) {
> for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
> if (drm_atomic_crtc_needs_modeset(new_crtc_state)) {
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index f26887c3fe8b194137200f9f2426653274c50fda..2c62840416f4b807d6a880b5c30ae024a16af528 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -433,6 +433,7 @@ mode_fixup(struct drm_atomic_state *state)
>
> for_each_new_connector_in_state(state, connector, new_conn_state, i) {
> const struct drm_encoder_helper_funcs *funcs;
> + bool old_needs_modeset = false;
> struct drm_encoder *encoder;
> struct drm_bridge *bridge;
>
> @@ -451,6 +452,9 @@ mode_fixup(struct drm_atomic_state *state)
> encoder = new_conn_state->best_encoder;
> funcs = encoder->helper_private;
>
> + if (new_crtc_state)
> + old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> bridge = drm_bridge_chain_get_first_bridge(encoder);
> ret = drm_atomic_bridge_chain_check(bridge,
> new_crtc_state,
> @@ -479,6 +483,12 @@ mode_fixup(struct drm_atomic_state *state)
> return -EINVAL;
> }
> }
> +
> + if (new_crtc_state) {
> + bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> + state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
> + }
> }
>
> for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
> @@ -574,6 +584,36 @@ mode_valid(struct drm_atomic_state *state)
> return 0;
> }
>
> +static int
> +connector_atomic_check(struct drm_atomic_state *state,
> + struct drm_connector *connector,
> + struct drm_connector_state *old_connector_state,
> + struct drm_connector_state *new_connector_state)
> +{
> + const struct drm_connector_helper_funcs *funcs = connector->helper_private;
> + struct drm_crtc_state *new_crtc_state;
> + bool old_needs_modeset = false;
> + int ret;
> +
> + if (new_connector_state->crtc)
> + new_crtc_state = drm_atomic_get_new_crtc_state(state, new_connector_state->crtc);
> + if (new_crtc_state)
> + old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> + if (funcs->atomic_check)
> + ret = funcs->atomic_check(connector, state);
> + else
> + ret = 0;
> +
> + if (new_crtc_state) {
> + bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> + state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
> + }
> +
> + return ret;
> +}
> +
> /**
> * drm_atomic_helper_check_modeset - validate state object for modeset changes
> * @dev: DRM device
> @@ -628,6 +668,8 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
> int i, ret;
> unsigned int connectors_mask = 0, user_connectors_mask = 0;
>
> + state->dirty_needs_modeset = false;
> +
> for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i)
> user_connectors_mask |= BIT(i);
>
> @@ -683,8 +725,6 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
> return ret;
>
> for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
> - const struct drm_connector_helper_funcs *funcs = connector->helper_private;
> -
> WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>
> /*
> @@ -710,8 +750,8 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
> new_crtc_state->connectors_changed = true;
> }
>
> - if (funcs->atomic_check)
> - ret = funcs->atomic_check(connector, state);
> + ret = connector_atomic_check(state, connector,
> + old_connector_state, new_connector_state);
> if (ret) {
> drm_dbg_atomic(dev,
> "[CONNECTOR:%d:%s] driver check failed\n",
> @@ -752,13 +792,11 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
> * has been called on them when a modeset is forced.
> */
> for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
> - const struct drm_connector_helper_funcs *funcs = connector->helper_private;
> -
> if (connectors_mask & BIT(i))
> continue;
>
> - if (funcs->atomic_check)
> - ret = funcs->atomic_check(connector, state);
> + ret = connector_atomic_check(state, connector,
> + old_connector_state, new_connector_state);
> if (ret) {
> drm_dbg_atomic(dev,
> "[CONNECTOR:%d:%s] driver check failed\n",
> @@ -994,6 +1032,7 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
>
> for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
> const struct drm_plane_helper_funcs *funcs;
> + bool old_needs_modeset = false;
>
> WARN_ON(!drm_modeset_is_locked(&plane->mutex));
>
> @@ -1006,6 +1045,12 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
> if (!funcs || !funcs->atomic_check)
> continue;
>
> + if (new_plane_state->crtc)
> + new_crtc_state = drm_atomic_get_new_crtc_state(state,
> + new_plane_state->crtc);
> + if (new_crtc_state)
> + old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> ret = funcs->atomic_check(plane, state);
> if (ret) {
> drm_dbg_atomic(plane->dev,
> @@ -1013,16 +1058,26 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
> plane->base.id, plane->name);
> return ret;
> }
> +
> + if (new_crtc_state) {
> + bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> + state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
> + }
> }
>
> for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
> const struct drm_crtc_helper_funcs *funcs;
> + bool old_needs_modeset = false;
>
> funcs = crtc->helper_private;
>
> if (!funcs || !funcs->atomic_check)
> continue;
>
> + if (new_crtc_state)
> + old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> ret = funcs->atomic_check(crtc, state);
> if (ret) {
> drm_dbg_atomic(crtc->dev,
> @@ -1030,6 +1085,12 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
> crtc->base.id, crtc->name);
> return ret;
> }
> +
> + if (new_crtc_state) {
> + bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
> +
> + state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
> + }
> }
>
> return ret;
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 31ca88deb10d262fb3a3f8e14d2afe24f8410cb1..7b0dbd3c8a3df340399a458aaf79263f0fdc24e5 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -408,6 +408,16 @@ struct drm_atomic_state {
> */
> bool duplicated : 1;
>
> + /**
> + * @dirty_needs_modeset:
> + *
> + * Indicates whether the drm_atomic_crtc_needs_modeset() changed in an
> + * unexpected way. Usually this means that driver implements atomic
> + * helpers using drm_atomic_crtc_needs_modeset(), but mode_changed has
> + * toggled by one of its atomic_check() callbacks.
> + */
> + bool dirty_needs_modeset : 1;
> +
> /**
> * @planes:
> *
>
> --
> 2.39.5
>
--
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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