[PATCH v2 2/4] drm/dp_mst: Start tracking per-port VCPI allocations
Lyude Paul
lyude at redhat.com
Mon Oct 29 16:43:02 UTC 2018
On Mon, 2018-10-29 at 15:24 +0100, Daniel Vetter wrote:
> On Fri, Oct 26, 2018 at 04:35:47PM -0400, Lyude Paul wrote:
> > There has been a TODO waiting for quite a long time in
> > drm_dp_mst_topology.c:
> >
> > /* We cannot rely on port->vcpi.num_slots to update
> > * topology_state->avail_slots as the port may not exist if the parent
> > * branch device was unplugged. This should be fixed by tracking
> > * per-port slot allocation in drm_dp_mst_topology_state instead of
> > * depending on the caller to tell us how many slots to release.
> > */
> >
> > That's not the only reason we should fix this: forcing the driver to
> > track the VCPI allocations throughout a state's atomic check is
> > error prone, because it means that extra care has to be taken with the
> > order that drm_dp_atomic_find_vcpi_slots() and
> > drm_dp_atomic_release_vcpi_slots() are called in in order to ensure
> > idempotency. Currently the only driver actually using these helpers,
> > i915, doesn't even do this correctly: multiple ->best_encoder() checks
> > with i915's current implementation would not be idempotent and would
> > over-allocate VCPI slots, something I learned trying to implement
> > fallback retraining in MST.
> >
> > So: simplify this whole mess, and teach drm_dp_atomic_find_vcpi_slots()
> > and drm_dp_atomic_release_vcpi_slots() to track the VCPI allocations for
> > each port. This allows us to ensure idempotency without having to rely
> > on the driver as much. Additionally: the driver doesn't need to do any
> > kind of VCPI slot tracking anymore if it doesn't need it for it's own
> > internal state.
> >
> > Additionally; this adds a new drm_dp_mst_atomic_check() helper which
> > must be used by atomic drivers to perform validity checks for the new
> > VCPI allocations incurred by a state.
> >
> > Also: update the documentation and make it more obvious that these
> > /must/ be called by /all/ atomic drivers supporting MST.
> >
> > Changes since v1:
> > - Don't use the now-removed ->atomic_check() for private objects hook,
> > just give drivers a function to call themselves
> >
> > Signed-off-by: Lyude Paul <lyude at redhat.com>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > ---
> > drivers/gpu/drm/drm_dp_mst_topology.c | 190 +++++++++++++++++++++-----
> > drivers/gpu/drm/i915/intel_display.c | 8 ++
> > drivers/gpu/drm/i915/intel_dp_mst.c | 31 +++--
> > include/drm/drm_dp_mst_helper.h | 11 +-
> > 4 files changed, 192 insertions(+), 48 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 8c3cfac437f4..dcfab7536914 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -2614,21 +2614,33 @@ static int drm_dp_init_vcpi(struct
> > drm_dp_mst_topology_mgr *mgr,
> > }
> >
> > /**
> > - * drm_dp_atomic_find_vcpi_slots() - Find and add vcpi slots to the state
> > + * drm_dp_atomic_find_vcpi_slots() - Find and add VCPI slots to the state
> > * @state: global atomic state
> > * @mgr: MST topology manager for the port
> > * @port: port to find vcpi slots for
> > * @pbn: bandwidth required for the mode in PBN
> > *
> > + * Allocates VCPI slots to @port, replacing any previous VCPI allocations
> > it
> > + * may have had. Any atomic drivers which support MST must call this
> > function
> > + * in their atomic_check() handlers to change the current VCPI allocation
> > for
>
> Maybe do a nice kerneldoc reference to the right atomic_check here.
>
> > + * the new state. After the ->atomic_check() hooks of the driver and all
> > other
>
> This will upset the kerneldoc parser I think.
>
> > + * mode objects in the state have been called, DRM will check the final
> > VCPI
> > + * allocations to ensure that they will fit into the available bandwidth
> > on
> > + * the topology.
> > + *
> > + * See also: drm_dp_atomic_release_vcpi_slots()
>
> Also need to reference drm_dp_mst_atomic_check() here and that drivers
> must call it or nothing happens.
> > + *
> > * RETURNS:
> > - * Total slots in the atomic state assigned for this port or error
> > + * Total slots in the atomic state assigned for this port, or a negative
> > error
> > + * code if the port no longer exists
> > */
> > int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
> > struct drm_dp_mst_topology_mgr *mgr,
> > struct drm_dp_mst_port *port, int pbn)
> > {
> > struct drm_dp_mst_topology_state *topology_state;
> > - int req_slots;
> > + struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
> > + int prev_slots, req_slots, ret;
> >
> > topology_state = drm_atomic_get_mst_topology_state(state, mgr);
> > if (IS_ERR(topology_state))
> > @@ -2637,20 +2649,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
> > drm_atomic_state *state,
> > port = drm_dp_get_validated_port_ref(mgr, port);
> > if (port == NULL)
> > return -EINVAL;
> > - req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> > - DRM_DEBUG_KMS("vcpi slots req=%d, avail=%d\n",
> > - req_slots, topology_state->avail_slots);
> >
> > - if (req_slots > topology_state->avail_slots) {
> > - drm_dp_put_port(port);
> > - return -ENOSPC;
> > + /* Find the current allocation for this port, if any */
> > + list_for_each_entry(pos, &topology_state->vcpis, next) {
> > + if (pos->port == port) {
> > + vcpi = pos;
> > + prev_slots = vcpi->vcpi;
> > + break;
> > + }
> > }
> > + if (!vcpi)
> > + prev_slots = 0;
>
> For robustness should we warn here, since drivers forgetting to release
> vcpi slots is kinda a bug? Or do we need to have this to make life easier
> for driver writers?
Latter-mainly because we want to be able to make sure that when we add stuff
like fallback retraining, because then if we run into a case where we need to
recalculate the mode for a pipe more then once we have to make sure that every
driver is actually tracking what VCPI slots it requested, then also make sure
that every driver is mindful to release those VCPI slots on subsequent atomic
checks. IMO, it'd be redundant bookkeeping.
>
> > +
> > + req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> > +
> > + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] [MST PORT:%p] vcpi %d -> %d\n",
> > + port->connector->base.id, port->connector->name, port,
> > + prev_slots, req_slots);
> > +
> > + /* Add the new allocation to the state */
> > + if (!vcpi) {
> > + vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
> > + if (!vcpi) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> >
> > - topology_state->avail_slots -= req_slots;
> > - DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> > + vcpi->port = port;
> > + list_add(&vcpi->next, &topology_state->vcpis);
> > + }
> > + vcpi->vcpi = req_slots;
> >
> > + ret = req_slots;
> > +out:
> > drm_dp_put_port(port);
> > - return req_slots;
> > + return ret;
> > }
> > EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
> >
> > @@ -2658,32 +2691,46 @@ EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
> > * drm_dp_atomic_release_vcpi_slots() - Release allocated vcpi slots
> > * @state: global atomic state
> > * @mgr: MST topology manager for the port
> > - * @slots: number of vcpi slots to release
> > + *
> > + * Releases any VCPI slots that have been allocated to a port in the
> > atomic
> > + * state. Any atomic drivers which support MST must call this function in
> > + * their connector's atomic_check() handler when the connector will no
> > longer
> > + * have VCPI allocated (e.g. because it's CRTC was removed).
> > + *
> > + * It is OK to call this even if @port has been removed from the system,
> > in
> > + * which case it will just amount to a no-op.
> > + *
> > + * See also: drm_dp_atomic_find_vcpi_slots()
>
> Same comments as with the _find_vcpi_slots() function.
>
> > *
> > * RETURNS:
> > - * 0 if @slots were added back to &drm_dp_mst_topology_state->avail_slots
> > or
> > - * negative error code
> > + * 0 if all slots for this port were added back to
> > + * &drm_dp_mst_topology_state->avail_slots or negative error code
> > */
> > int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> > struct drm_dp_mst_topology_mgr *mgr,
> > - int slots)
> > + struct drm_dp_mst_port *port)
> > {
> > struct drm_dp_mst_topology_state *topology_state;
> > + struct drm_dp_vcpi_allocation *tmp, *pos;
> >
> > topology_state = drm_atomic_get_mst_topology_state(state, mgr);
> > if (IS_ERR(topology_state))
> > return PTR_ERR(topology_state);
> >
> > - /* We cannot rely on port->vcpi.num_slots to update
> > - * topology_state->avail_slots as the port may not exist if the parent
> > - * branch device was unplugged. This should be fixed by tracking
> > - * per-port slot allocation in drm_dp_mst_topology_state instead of
> > - * depending on the caller to tell us how many slots to release.
> > - */
> > - topology_state->avail_slots += slots;
> > - DRM_DEBUG_KMS("vcpi slots released=%d, avail=%d\n",
> > - slots, topology_state->avail_slots);
> > + list_for_each_entry_safe(pos, tmp, &topology_state->vcpis, next) {
> > + if (pos->port == port) {
> > + list_del(&pos->next);
> > + DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> > + port, pos->vcpi);
> >
> > + kfree(pos);
> > + return 0;
> > + }
> > + }
> > +
> > + /* If no allocation was found, all that means is that the port was
> > + * destroyed since the last atomic commit. That's OK!
> > + */
> > return 0;
> > }
> > EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> > @@ -3112,15 +3159,50 @@ static void drm_dp_destroy_connector_work(struct
> > work_struct *work)
> > static struct drm_private_state *
> > drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
> > {
> > - struct drm_dp_mst_topology_state *state;
> > + struct drm_dp_mst_topology_state *state, *old_state =
> > + to_dp_mst_topology_state(obj->state);
> > + struct drm_dp_mst_topology_mgr *mgr = old_state->mgr;
> > + struct drm_dp_mst_port *port;
> > + struct drm_dp_vcpi_allocation *pos, *vcpi;
> >
> > - state = kmemdup(obj->state, sizeof(*state), GFP_KERNEL);
> > + state = kzalloc(sizeof(*state), GFP_KERNEL);
> > if (!state)
> > return NULL;
> >
> > __drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
> >
> > + state->mgr = mgr;
> > + INIT_LIST_HEAD(&state->vcpis);
> > +
> > + /* Copy over the VCPI allocations for ports that still exist */
> > + list_for_each_entry(pos, &old_state->vcpis, next) {
> > + port = drm_dp_get_validated_port_ref(mgr, pos->port);
> > + if (!port) {
> > + DRM_DEBUG_ATOMIC("[MST PORT:%p] is gone, vcpi %d ->
> > 0\n",
> > + pos->port, pos->vcpi);
> > + continue;
> > + }
>
> Hm, in general we have 0 validation in the duplicate_state functions, Just
> dump copying, with minimal pointer/refcount updates.
> > +
> > + vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
>
> kmemdump + updating the list. Just in case we ever add more stuff here.
> Probably needs an explicit memset to avoid list debugging.
>
> At least that's the style we use everywhere else.
>
> > + if (!vcpi) {
> > + drm_dp_put_port(port);
> > + goto fail_alloc;
> > + }
> > +
> > + vcpi->port = port;
> > + vcpi->vcpi = pos->vcpi;
> > + list_add(&vcpi->next, &state->vcpis);
> > + drm_dp_put_port(port);
> > + }
> > +
> > return &state->base;
> > +
> > +fail_alloc:
> > + list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> > + kfree(pos);
> > + kfree(state);
> > +
> > + return NULL;
> > }
> >
> > static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> > @@ -3128,14 +3210,60 @@ 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_vcpi_allocation *pos, *tmp;
> > +
>
> WARN_ON(!list_empty());
>
> I think this not being empty on mgr teardown would be a driver bug. All
> the ports/branch devices should be gone by now, and also all the modeset
> state should have been torn down, using drm_atomic_helper_shutdown() or
> friends.
>
> > + list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next)
> > + kfree(pos);
> >
> > kfree(mst_state);
> > }
> >
> > -static const struct drm_private_state_funcs mst_state_funcs = {
> > +/**
> > + * drm_dp_mst_atomic_check - Check that the new state of an MST topology
> > in an
> > + * atomic update is valid
> > + * @state: Pointer to the new &struct drm_dp_mst_topology_state
> > + *
> > + * Checks the given topology state for an atomic update to ensure that
> > it's
> > + * valid. This includes checking whether there's enough bandwidth to
> > support
> > + * the new VCPI allocations in the atomic update.
> > + *
> > + * Any atomic drivers supporting DP MST must make sure to call this after
> > + * checking the rest of their state in their ->atomic_check() callback.
>
> &drm_mode_config_funcs.atomic_check
>
> > + *
> > + * Returns:
> > + *
> > + * 0 if the new state is valid, negative error code otherwise.
> > + */
> > +int drm_dp_mst_atomic_check(struct drm_dp_mst_topology_state *state)
> > +{
> > + struct drm_dp_mst_topology_mgr *mgr = state->mgr;
> > + struct drm_dp_vcpi_allocation *pos;
> > + int avail_slots = 63;
> > +
> > + list_for_each_entry(pos, &state->vcpis, next) {
> > + DRM_DEBUG_ATOMIC("[MST PORT:%p] requires %d vcpi slots\n",
> > + pos->port, pos->vcpi);
> > +
> > + avail_slots -= pos->vcpi;
> > + if (avail_slots < 0) {
> > + DRM_DEBUG_ATOMIC("[MST PORT:%p] not enough vcpi slots
> > in state %p (avail=%d)\n",
> > + pos->port, state,
> > + avail_slots + pos->vcpi);
> > + return -ENOSPC;
> > + }
> > + }
> > + DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p vcpi avail=%d used=%d\n",
> > + mgr, state, avail_slots, 63 - avail_slots);
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_mst_atomic_check);
>
> Commented on patch 4 already, but I think this would look a bit simpler if
> we (also/instead, up to you really) expose a helper that checks all mgr in
> a drm_atomic_state. No need to have the exact same loop in each driver.
>
> > +
> > +const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
> > .atomic_duplicate_state = drm_dp_mst_duplicate_state,
> > .atomic_destroy_state = drm_dp_mst_destroy_state,
> > };
> > +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
> >
> > /**
> > * drm_atomic_get_mst_topology_state: get MST topology state
> > @@ -3213,13 +3341,11 @@ int drm_dp_mst_topology_mgr_init(struct
> > drm_dp_mst_topology_mgr *mgr,
> > return -ENOMEM;
> >
> > mst_state->mgr = mgr;
> > -
> > - /* max. time slots - one slot for MTP header */
> > - mst_state->avail_slots = 63;
> > + INIT_LIST_HEAD(&mst_state->vcpis);
> >
> > drm_atomic_private_obj_init(&mgr->base,
> > &mst_state->base,
> > - &mst_state_funcs);
> > + &drm_dp_mst_topology_state_funcs);
> >
> > return 0;
> > }
> > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > b/drivers/gpu/drm/i915/intel_display.c
> > index fe045abb6472..f66af1465686 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -12484,6 +12484,8 @@ static int intel_atomic_check(struct drm_device
> > *dev,
> > struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
> > struct drm_crtc *crtc;
> > struct drm_crtc_state *old_crtc_state, *crtc_state;
> > + struct drm_dp_mst_topology_mgr *mgr;
> > + struct drm_dp_mst_topology_state *mst_state;
> > int ret, i;
> > bool any_ms = false;
> >
> > @@ -12534,6 +12536,12 @@ static int intel_atomic_check(struct drm_device
> > *dev,
> > "[modeset]" : "[fastset]");
> > }
> >
> > + for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
> > + ret = drm_dp_mst_atomic_check(mst_state);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > if (any_ms) {
> > ret = intel_modeset_checks(state);
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c
> > b/drivers/gpu/drm/i915/intel_dp_mst.c
> > index 8b71d64ebd9d..aaf904738b78 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct
> > drm_connector *connector,
> > struct drm_connector_state *old_conn_state;
> > struct drm_crtc *old_crtc;
> > struct drm_crtc_state *crtc_state;
> > - int slots, ret = 0;
> > + struct intel_connector *intel_connector =
> > + to_intel_connector(connector);
> > + struct drm_dp_mst_topology_mgr *mgr =
> > + &intel_connector->mst_port->mst_mgr;
> > + struct drm_dp_mst_port *port = intel_connector->port;
> > + int ret = 0;
> >
> > old_conn_state = drm_atomic_get_old_connector_state(state, connector);
> > old_crtc = old_conn_state->crtc;
> > if (!old_crtc)
> > return ret;
> >
> > - crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> > - slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
> > - if (drm_atomic_crtc_needs_modeset(crtc_state) && slots > 0) {
> > - struct drm_dp_mst_topology_mgr *mgr;
> > - struct drm_encoder *old_encoder;
> > + /* Free VCPI, since compute_config() won't be run */
> > + if (!new_conn_state->crtc) {
> > + crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> >
> > - old_encoder = old_conn_state->best_encoder;
> > - mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> > -
> > - ret = drm_dp_atomic_release_vcpi_slots(state, mgr, slots);
> > - if (ret)
> > - DRM_DEBUG_KMS("failed releasing %d vcpi slots:%d\n",
> > slots, ret);
> > - else
> > - to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> > + ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> > + if (ret) {
> > + DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
> > + ret);
> > + return ret;
> > + }
> > + to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> > }
> > +
> > return ret;
> > }
> >
> > diff --git a/include/drm/drm_dp_mst_helper.h
> > b/include/drm/drm_dp_mst_helper.h
> > index 3faceb66f5cb..0aa7d3658013 100644
> > --- a/include/drm/drm_dp_mst_helper.h
> > +++ b/include/drm/drm_dp_mst_helper.h
> > @@ -406,9 +406,15 @@ struct drm_dp_payload {
> >
> > #define to_dp_mst_topology_state(x) container_of(x, struct
> > drm_dp_mst_topology_state, base)
> >
> > +struct drm_dp_vcpi_allocation {
> > + struct drm_dp_mst_port *port;
> > + int vcpi;
> > + struct list_head next;
> > +};
> > +
> > struct drm_dp_mst_topology_state {
> > struct drm_private_state base;
> > - int avail_slots;
> > + struct list_head vcpis;
> > struct drm_dp_mst_topology_mgr *mgr;
> > };
> >
> > @@ -624,9 +630,10 @@ int drm_dp_atomic_find_vcpi_slots(struct
> > drm_atomic_state *state,
> > struct drm_dp_mst_port *port, int pbn);
>
> I think annotating the relase/find functions with __must_check would be
> good.
>
> > int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> > struct drm_dp_mst_topology_mgr *mgr,
> > - int slots);
> > + struct drm_dp_mst_port *port);
> > int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
> > struct drm_dp_mst_port *port, bool power_up);
>
> Same here.
>
> > +int drm_dp_mst_atomic_check(struct drm_dp_mst_topology_state *state);
>
> With the nits addressed:
>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>
> >
> > extern const struct drm_private_state_funcs
> > drm_dp_mst_topology_state_funcs;
> >
> > --
> > 2.17.2
> >
>
>
--
Cheers,
Lyude Paul
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