[RESEND RFC 08/18] drm/display/dp_mst: Add nonblocking helpers for DP MST

Lyude Paul
2022-06-08T01:47:10Z

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@redhat.com>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Fangzhi Zuo <Jerry.Zuo@amd.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <sean@poorly.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);
+}

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,
--
2.35.3