Date:   Wed, 29 Jun 2022 16:30:28 +0300
From:   Jani Nikula <jani.nikula@...el.com>
To:     Lyude Paul <lyude@...hat.com>, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org
Cc:     Wayne Lin <Wayne.Lin@....com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Fangzhi Zuo <Jerry.Zuo@....com>,
        Imre Deak <imre.deak@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sean Paul <sean@...rly.run>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Roman Li <Roman.Li@....com>, Jude Shih <shenshih@....com>,
        Simon Ser <contact@...rsion.fr>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Manasi Navare <manasi.d.navare@...el.com>,
        José Roberto de Souza <jose.souza@...el.com>,
        Dave Airlie <airlied@...hat.com>,
        Sean Paul <seanpaul@...omium.org>,
        Fernando Ramos <greenfoo@....eu>,
        Javier Martinez Canillas <javierm@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:INTEL DRM DRIVERS" <intel-gfx@...ts.freedesktop.org>
Subject: Re: [RESEND RFC 08/18] drm/display/dp_mst: Add nonblocking helpers
 for DP MST

On Tue, 07 Jun 2022, Lyude Paul <lyude@...hat.com> wrote:
> As Daniel Vetter pointed out, if we only use the atomic modesetting locks
> with MST it's technically possible for a driver with non-blocking modesets
> to race when it comes to MST displays - as we make the mistake of not doing
> our own CRTC commit tracking in the topology_state object.
>
> This could potentially cause problems if something like this happens:
>
> * User starts non-blocking commit to disable CRTC-1 on MST topology 1
> * User starts non-blocking commit to enable CRTC-2 on MST topology 1
>
> There's no guarantee here that the commit for disabling CRTC-2 will only
> occur after CRTC-1 has finished, since neither commit shares a CRTC - only
> the private modesetting object for MST. Keep in mind this likely isn't a
> problem for blocking modesets, only non-blocking.
>
> So, begin fixing this by keeping track of which CRTCs on a topology have
> changed by keeping track of which CRTCs we release or allocate timeslots
> on. As well, add some helpers for:
>
> * Setting up the drm_crtc_commit structs in the ->commit_setup hook
> * Waiting for any CRTC dependencies from the previous topology state
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Cc: Wayne Lin <Wayne.Lin@....com>
> Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Cc: Fangzhi Zuo <Jerry.Zuo@....com>
> Cc: Jani Nikula <jani.nikula@...el.com>
> Cc: Imre Deak <imre.deak@...el.com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: Sean Paul <sean@...rly.run>
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  9 +-
>  drivers/gpu/drm/display/drm_dp_mst_topology.c | 93 +++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_display.c  | 11 +++
>  drivers/gpu/drm/nouveau/dispnv50/disp.c       | 12 +++
>  include/drm/display/drm_dp_mst_helper.h       | 15 +++
>  5 files changed, 139 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index f84a4ad736d8..d9c7393ef151 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -211,6 +211,7 @@ static int amdgpu_dm_encoder_init(struct drm_device *dev,
>  static int amdgpu_dm_connector_get_modes(struct drm_connector *connector);
>  
>  static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state);
> +static int amdgpu_dm_atomic_setup_commit(struct drm_atomic_state *state);
>  
>  static int amdgpu_dm_atomic_check(struct drm_device *dev,
>  				  struct drm_atomic_state *state);
> @@ -2808,7 +2809,8 @@ static const struct drm_mode_config_funcs amdgpu_dm_mode_funcs = {
>  };
>  
>  static struct drm_mode_config_helper_funcs amdgpu_dm_mode_config_helperfuncs = {
> -	.atomic_commit_tail = amdgpu_dm_atomic_commit_tail
> +	.atomic_commit_tail = amdgpu_dm_atomic_commit_tail,
> +	.atomic_commit_setup = amdgpu_dm_atomic_setup_commit,
>  };
>  
>  static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
> @@ -9558,6 +9560,7 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
>  		DRM_ERROR("Waiting for fences timed out!");
>  
>  	drm_atomic_helper_update_legacy_modeset_state(dev, state);
> +	drm_dp_mst_atomic_wait_for_dependencies(state);
>  
>  	dm_state = dm_atomic_get_new_state(state);
>  	if (dm_state && dm_state->context) {
> @@ -9958,6 +9961,10 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
>  		dc_release_state(dc_state_temp);
>  }
>  
> +static int amdgpu_dm_atomic_setup_commit(struct drm_atomic_state *state)
> +{
> +	return drm_dp_mst_atomic_setup_commit(state);
> +}

I guess all the driver specific wrappers for setup commit could be
dropped in favor of directly using drm_dp_mst_atomic_setup_commit?

BR,
Jani.

>  
>  static int dm_force_atomic_commit(struct drm_connector *connector)
>  {
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 0bc2c7a90c37..a0ed29f83556 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -4395,12 +4395,16 @@ int drm_dp_atomic_find_time_slots(struct drm_atomic_state *state,
>  {
>  	struct drm_dp_mst_topology_state *topology_state;
>  	struct drm_dp_mst_atomic_payload *payload = NULL;
> +	struct drm_connector_state *conn_state;
>  	int prev_slots = 0, prev_bw = 0, req_slots;
>  
>  	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
>  	if (IS_ERR(topology_state))
>  		return PTR_ERR(topology_state);
>  
> +	conn_state = drm_atomic_get_new_connector_state(state, port->connector);
> +	topology_state->pending_crtc_mask |= drm_crtc_mask(conn_state->crtc);
> +
>  	/* Find the current allocation for this port, if any */
>  	payload = drm_atomic_get_mst_payload_state(topology_state, port);
>  	if (payload) {
> @@ -4480,11 +4484,15 @@ int drm_dp_atomic_release_time_slots(struct drm_atomic_state *state,
>  {
>  	struct drm_dp_mst_topology_state *topology_state;
>  	struct drm_dp_mst_atomic_payload *payload;
> +	struct drm_connector_state *conn_state;
>  
>  	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
>  	if (IS_ERR(topology_state))
>  		return PTR_ERR(topology_state);
>  
> +	conn_state = drm_atomic_get_old_connector_state(state, port->connector);
> +	topology_state->pending_crtc_mask |= drm_crtc_mask(conn_state->crtc);
> +
>  	payload = drm_atomic_get_mst_payload_state(topology_state, port);
>  	if (WARN_ON(!payload)) {
>  		drm_err(mgr->dev, "No payload for [MST PORT:%p] found in mst state %p\n",
> @@ -4503,6 +4511,83 @@ int drm_dp_atomic_release_time_slots(struct drm_atomic_state *state,
>  }
>  EXPORT_SYMBOL(drm_dp_atomic_release_time_slots);
>  
> +/**
> + * drm_dp_mst_atomic_setup_commit() - setup_commit hook for MST helpers
> + * @state: global atomic state
> + *
> + * This function saves all of the &drm_crtc_commit structs in an atomic state that touch any CRTCs
> + * currently assigned to an MST topology. Drivers must call this hook from their
> + * &drm_mode_config_helper_funcs.atomic_commit_setup hook.
> + *
> + * Returns:
> + * 0 if all CRTC commits were retrieved successfully, negative error code otherwise
> + */
> +int drm_dp_mst_atomic_setup_commit(struct drm_atomic_state *state)
> +{
> +	struct drm_dp_mst_topology_mgr *mgr;
> +	struct drm_dp_mst_topology_state *mst_state;
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *crtc_state;
> +	int i, j, commit_idx, num_commit_deps;
> +
> +	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
> +		if (!mst_state->pending_crtc_mask)
> +			continue;
> +
> +		num_commit_deps = hweight32(mst_state->pending_crtc_mask);
> +		mst_state->commit_deps = kmalloc_array(num_commit_deps,
> +						       sizeof(*mst_state->commit_deps), GFP_KERNEL);
> +		if (!mst_state->commit_deps)
> +			return -ENOMEM;
> +		mst_state->num_commit_deps = num_commit_deps;
> +
> +		commit_idx = 0;
> +		for_each_new_crtc_in_state(state, crtc, crtc_state, j) {
> +			if (mst_state->pending_crtc_mask & drm_crtc_mask(crtc)) {
> +				mst_state->commit_deps[commit_idx++] =
> +					drm_crtc_commit_get(crtc_state->commit);
> +			}
> +		}
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_mst_atomic_setup_commit);
> +
> +/**
> + * drm_dp_mst_atomic_wait_for_dependencies() - Wait for all pending commits on MST topologies
> + * @state: global atomic state
> + *
> + * Goes through any MST topologies in this atomic state, and waits for any pending commits which
> + * touched CRTCs that were/are on an MST topology to be programmed to hardware and flipped to before
> + * returning. This is to prevent multiple non-blocking commits affecting an MST topology from racing
> + * with eachother by forcing them to be executed sequentially in situations where the only resources
> + * the modeset objects in these commits share are an MST topology.
> + *
> + * This function also prepares the new MST state for commit by performing some state preparation
> + * which can't be done until this point, such as reading back the final VC start slots (which are
> + * determined at commit-time) from the previous state.
> + *
> + * All MST drivers must call this function after calling drm_atomic_helper_wait_for_dependencies(),
> + * or whatever their equivalent of that is.
> + */
> +void drm_dp_mst_atomic_wait_for_dependencies(struct drm_atomic_state *state)
> +{
> +	struct drm_dp_mst_topology_state *old_mst_state;
> +	struct drm_dp_mst_topology_mgr *mgr;
> +	int i, j, ret;
> +
> +	for_each_old_mst_mgr_in_state(state, mgr, old_mst_state, i) {
> +		for (j = 0; j < old_mst_state->num_commit_deps; j++) {
> +			ret = drm_crtc_commit_wait(old_mst_state->commit_deps[j]);
> +			if (ret < 0)
> +				drm_err(state->dev, "Failed to wait for %s: %d\n",
> +					old_mst_state->commit_deps[j]->crtc->name, ret);
> +		}
> +	}
> +}
> +EXPORT_SYMBOL(drm_dp_mst_atomic_wait_for_dependencies);
> +
>  /**
>   * drm_dp_mst_update_slots() - updates the slot info depending on the DP ecoding format
>   * @mst_state: mst_state to update
> @@ -5079,6 +5164,9 @@ drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
>  	__drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
>  
>  	INIT_LIST_HEAD(&state->payloads);
> +	state->commit_deps = NULL;
> +	state->num_commit_deps = 0;
> +	state->pending_crtc_mask = 0;
>  
>  	list_for_each_entry(pos, &old_state->payloads, next) {
>  		/* Prune leftover freed timeslot allocations */
> @@ -5111,6 +5199,7 @@ static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
>  	struct drm_dp_mst_topology_state *mst_state =
>  		to_dp_mst_topology_state(state);
>  	struct drm_dp_mst_atomic_payload *pos, *tmp;
> +	int i;
>  
>  	list_for_each_entry_safe(pos, tmp, &mst_state->payloads, next) {
>  		/* We only keep references to ports with non-zero VCPIs */
> @@ -5119,6 +5208,10 @@ static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
>  		kfree(pos);
>  	}
>  
> +	for (i = 0; i < mst_state->num_commit_deps; i++)
> +		drm_crtc_commit_put(mst_state->commit_deps[i]);
> +
> +	kfree(mst_state->commit_deps);
>  	kfree(mst_state);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 186b37925d23..5475f66c0ed8 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -8446,6 +8446,7 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
>  	intel_atomic_commit_fence_wait(state);
>  
>  	drm_atomic_helper_wait_for_dependencies(&state->base);
> +	drm_dp_mst_atomic_wait_for_dependencies(&state->base);
>  
>  	if (state->modeset)
>  		wakeref = intel_display_power_get(dev_priv, POWER_DOMAIN_MODESET);
> @@ -9514,6 +9515,15 @@ static int intel_initial_commit(struct drm_device *dev)
>  	return ret;
>  }
>  
> +static int intel_atomic_commit_setup(struct drm_atomic_state *state)
> +{
> +	return drm_dp_mst_atomic_setup_commit(state);
> +}
> +
> +static const struct drm_mode_config_helper_funcs intel_mode_config_funcs = {
> +	.atomic_commit_setup = intel_atomic_commit_setup,
> +};
> +
>  static void intel_mode_config_init(struct drm_i915_private *i915)
>  {
>  	struct drm_mode_config *mode_config = &i915->drm.mode_config;
> @@ -9528,6 +9538,7 @@ static void intel_mode_config_init(struct drm_i915_private *i915)
>  	mode_config->prefer_shadow = 1;
>  
>  	mode_config->funcs = &intel_mode_funcs;
> +	mode_config->helper_private = &intel_mode_config_funcs;
>  
>  	mode_config->async_page_flip = HAS_ASYNC_FLIPS(i915);
>  
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index 631dba5a2418..768312607fdb 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -2134,6 +2134,7 @@ nv50_disp_atomic_commit_tail(struct drm_atomic_state *state)
>  	nv50_crc_atomic_stop_reporting(state);
>  	drm_atomic_helper_wait_for_fences(dev, state, false);
>  	drm_atomic_helper_wait_for_dependencies(state);
> +	drm_dp_mst_atomic_wait_for_dependencies(state);
>  	drm_atomic_helper_update_legacy_modeset_state(dev, state);
>  	drm_atomic_helper_calc_timestamping_constants(state);
>  
> @@ -2614,6 +2615,16 @@ nv50_disp_func = {
>  	.atomic_state_free = nv50_disp_atomic_state_free,
>  };
>  
> +static int nv50_disp_atomic_setup_commit(struct drm_atomic_state *state)
> +{
> +	return drm_dp_mst_atomic_setup_commit(state);
> +}
> +
> +static const struct drm_mode_config_helper_funcs
> +nv50_disp_helper_func = {
> +	.atomic_commit_setup = nv50_disp_atomic_setup_commit,
> +};
> +
>  /******************************************************************************
>   * Init
>   *****************************************************************************/
> @@ -2713,6 +2724,7 @@ nv50_display_create(struct drm_device *dev)
>  	nouveau_display(dev)->fini = nv50_display_fini;
>  	disp->disp = &nouveau_display(dev)->disp;
>  	dev->mode_config.funcs = &nv50_disp_func;
> +	dev->mode_config.helper_private = &nv50_disp_helper_func;
>  	dev->mode_config.quirk_addfb_prefer_xbgr_30bpp = true;
>  	dev->mode_config.normalize_zpos = true;
>  
> diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
> index eb0ea578b227..dd74afcee888 100644
> --- a/include/drm/display/drm_dp_mst_helper.h
> +++ b/include/drm/display/drm_dp_mst_helper.h
> @@ -576,6 +576,19 @@ struct drm_dp_mst_topology_state {
>  	/** @mgr: The topology manager */
>  	struct drm_dp_mst_topology_mgr *mgr;
>  
> +	/**
> +	 * @pending_crtc_mask: A bitmask of all CRTCs this topology state touches, drivers may
> +	 * modify this to add additional dependencies if needed.
> +	 */
> +	u32 pending_crtc_mask;
> +	/**
> +	 * @commit_deps: A list of all CRTC commits affecting this topology, this field isn't
> +	 * populated until drm_dp_mst_atomic_wait_for_dependencies() is called.
> +	 */
> +	struct drm_crtc_commit **commit_deps;
> +	/** @num_commit_deps: The number of CRTC commits in @commit_deps */
> +	size_t num_commit_deps;
> +
>  	/** @total_avail_slots: The total number of slots this topology can handle (63 or 64) */
>  	u8 total_avail_slots;
>  	/** @start_slot: The first usable time slot in this topology (1 or 0) */
> @@ -885,6 +898,8 @@ int __must_check
>  drm_dp_atomic_release_time_slots(struct drm_atomic_state *state,
>  				 struct drm_dp_mst_topology_mgr *mgr,
>  				 struct drm_dp_mst_port *port);
> +void drm_dp_mst_atomic_wait_for_dependencies(struct drm_atomic_state *state);
> +int __must_check drm_dp_mst_atomic_setup_commit(struct drm_atomic_state *state);
>  int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
>  				 struct drm_dp_mst_port *port, bool power_up);
>  int drm_dp_send_query_stream_enc_status(struct drm_dp_mst_topology_mgr *mgr,

-- 
Jani Nikula, Intel Open Source Graphics Center

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