On Mon, Nov 26, 2018 at 04:36:46PM -0500, Lyude Paul wrote:
> On Mon, 2018-11-26 at 22:04 +0100, Daniel Vetter wrote:
> > On Thu, Nov 15, 2018 at 07:50:05PM -0500, 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 v6:
> > > - Keep a kref to all of the ports we have allocations on. This required
> > > a good bit of changing to when we call drm_dp_find_vcpi_slots(),
> > > mainly that we need to ensure that we only redo VCPI allocations on
> > > actual mode or CRTC changes, not crtc_state->active changes.
> > > Additionally, we no longer take the registration of the DRM connector
> > > for each port into account because so long as we have a kref to the
> > > port in the new or previous atomic state, the connector will stay
> > > registered.
> >
> > I write an entire pile of small nitpits (still included most of them
> > below), until I realized this here wont work. Delaying the call to destroy
> > the connector (well, unregister it really) wreaks the design we've come up
> > with thus far, resulting in most of my comments here.
> >
> > Instead, all we need to do is delay the kfree(port) at the bottom of
> > drm_dp_destroy_port(). The vcpi allocation structure _only_ needs the
> > pointer value to stay valid, as a lookup key. It doesn't care at all about
> > anything actually stored in there. So the only thing we need to delay is
> > the kfree. I think the simplest way to achieve this is to add a 2nd kref
> > (port->kfree_ref or something like that), with on reference held by the
> > port itself (released in drm_dp_destroy_port), and the other one held
> > as-needed by the vcpi allocation lists.
> >
> > I think if we go with this design instead of retrofitting a semantic
> > change of the port lifetime itself, all the complications I complain about
> > below should disappear.
> >
> > Piles of comments below.
> >
> > Cheers, Daniel
> >
> > > - Use the small changes to drm_dp_put_port() to add even more error
> > > checking to make misusage of the helpers more obvious. I added this
> > > after having to chase down various use-after-free conditions that
> > > started popping up from the new helpers so no one else has to
> > > troubleshoot that.
> > > - Move some accidental DRM_DEBUG_KMS() calls to DRM_DEBUG_ATOMIC()
> > > - Update documentation again, note that find/release() should both not be
> > > called on the same port in a single atomic check phase (but multiple
> > > calls to one or the other is OK)
> > >
> > > Changes since v4:
> > > - Don't skip the atomic checks for VCPI allocations if no new VCPI
> > > allocations happen in a state. This makes the next change I'm about
> > > to list here a lot easier to implement.
> > > - Don't ignore VCPI allocations on destroyed ports, instead ensure that
> > > when ports are destroyed and still have VCPI allocations in the
> > > topology state, the only state changes allowed are releasing said
> > > ports' VCPI. This prevents a state with a mix of VCPI allocations
> > > from destroyed ports, and allocations from valid ports.
> > >
> > > Changes since v3:
> > > - Don't release VCPI allocations in the topology state immediately in
> > > drm_dp_atomic_release_vcpi_slots(), instead mark them as 0 and skip
> > > over them in drm_dp_mst_duplicate_state(). This makes it so
> > > drm_dp_atomic_release_vcpi_slots() is still idempotent while also
> > > throwing warnings if the driver messes up it's book keeping and tries
> > > to release VCPI slots on a port that doesn't have any pre-existing
> > > VCPI allocation - danvet
> > > - Change mst_state/state in some debugging messages to "mst state"
> > >
> > > Changes since v2:
> > > - Use kmemdup() for duplicating MST state - danvet
> > > - Move port validation out of duplicate state callback - danvet
> > > - Handle looping through MST topology states in
> > > drm_dp_mst_atomic_check() so the driver doesn't have to do it
> > > - Fix documentation in drm_dp_atomic_find_vcpi_slots()
> > > - Move the atomic check for each individual topology state into it's
> > > own function, reduces indenting
> > > - Don't consider "stale" MST ports when calculating the bandwidth
> > > requirements. This is needed because originally we relied on the
> > > state duplication functions to prune any stale ports from the new
> > > state, which would prevent us from incorrectly considering their
> > > bandwidth requirements alongside legitimate new payloads.
> > > - Add function references in drm_dp_atomic_release_vcpi_slots() - danvet
> > > - Annotate atomic VCPI and atomic check functions with __must_check
> > > - danvet
> > >
> > > 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@xxxxxxxxxx>
> > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > > ---
> > > drivers/gpu/drm/drm_dp_mst_topology.c | 294 +++++++++++++++++++++++---
> > > drivers/gpu/drm/i915/intel_display.c | 4 +
> > > drivers/gpu/drm/i915/intel_dp_mst.c | 64 +++---
> > > include/drm/drm_dp_mst_helper.h | 24 ++-
> > > 4 files changed, 319 insertions(+), 67 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index 00fbe7a2699d..183d0e832ced 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -2617,21 +2617,42 @@ 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
> > > *
> > > - * RETURNS:
> > > - * Total slots in the atomic state assigned for this port or error
> > > + * 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 &drm_encoder_helper_funcs.atomic_check() callback to change
> > > the
> > > + * current VCPI allocation for the new state, but only when
> > > + * &drm_crtc_state.mode_changed or &drm_crtc_state.connectors_changed is
> > > set
> > > + * to ensure compatibility with userspace applications that still use the
> > > + * legacy modesetting UAPI.
> > > + *
> > > + * Allocations set by this function are not checked against the bandwidth
> > > + * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
> > > + *
> > > + * Additionally, it is OK to call this function multiple times on the
> > > same
> > > + * @port as needed. It is not OK however, to call this function and
> > > + * drm_dp_atomic_release_vcpi_slots() in the same atomic check phase.
> > > + *
> > > + * See also:
> > > + * drm_dp_atomic_release_vcpi_slots()
> > > + * drm_dp_mst_atomic_check()
> > > + *
> > > + * Returns:
> > > + * 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))
> > > @@ -2640,20 +2661,60 @@ 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;
> > > + topology_state->vcpi_allocated = true;
> > > +
> > > + /* 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;
> > > +
> > > + /*
> > > + * This should never happen, unless the driver tries
> > > + * releasing and allocating the same VCPI allocation,
> > > + * which is an error
> > > + */
> > > + if (WARN_ON(!prev_slots)) {
> > > + DRM_ERROR("cannot allocate and release VCPI on
> > > [MST PORT:%p] in the same state\n",
> > > + port);
> > > + return -EINVAL;
> > > + }
> >
> > Allowing atomic changes to output state (like disabling it on one crtc,
> > and then enabling on the other, thus both releasing and re-allocating the
> > vcpi in one go) is kinda the point of atomic. So definitely can't EINVAL
> > here.
> Actually-so long the original assertion we had of not allowing "stale" (e.g.
> VCPIs from now-destroyed topologies) VCPI allocations and real VCPI
> allocations in the same atomic state is held true, this should be fine.
>
> So: (and this answers the question below as well), the way this is supposed to
> work is that we just skip the whole VCPI validation sequence unless part of
> the state actually tried to add VCPI. This means userland can still disable
> displays one-by-one or set them as inactive, so long as it doesn't try to
> enable new MST displays until the point at which it's disabled everything
> leftover from the previous topology - since disabling displays won't allocate
> VCPI and thus skips the port validation checks here.
This doesn't sound robust if there's a race, e.g. userspace tries to light
up a display right at the time when we unplug a different (already enabled
output). I think to fix this properly we need to replace all the
dp_get_validated_port calls in all the vcpi/payload places with the
lower-level kref that only prevents the kfree.
Fundamentally hotunplug is still racy, but this way I think there's at
least no surprises. And we could probably remove a bunch of the hacks
around cleanup paths.
> > Sounds like we need more testcases in igt?
> >
> > > +
> > > + break;
> > > + }
> > > }
> > > + if (!vcpi)
> > > + prev_slots = 0;
> > >
> > > - topology_state->avail_slots -= req_slots;
> > > - DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> > > + req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> > > +
> > > + DRM_DEBUG_ATOMIC("[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;
> > > + }
> > >
> > > + vcpi->port = drm_dp_get_validated_port_ref(mgr, port);
> > > + if (!vcpi->port) {
> > > + ret = -EINVAL;
> > > + kfree(vcpi);
> > > + goto out;
> > > + }
> > > + 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);
> > >
> > > @@ -2661,31 +2722,66 @@ 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
> > > + * @port: The port to release the VCPI slots from
> > > *
> > > - * RETURNS:
> > > - * 0 if @slots were added back to &drm_dp_mst_topology_state->avail_slots
> > > or
> > > - * negative error code
> > > + * 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 &drm_connector_helper_funcs.atomic_check() callback when the
> > > + * connector will no longer have VCPI allocated (e.g. because it's CRTC
> > > was
> > > + * removed) when it had VCPI allocated in the previous atomic state.
> > > + *
> > > + * It is OK to call this even if @port has been removed from the system.
> > > + * Additionally, it is OK to call this function multiple times on the
> > > same
> > > + * @port as needed. It is not OK however, to call this function and
> > > + * drm_dp_atomic_find_vcpi_slots() on the same @port in a single atomic
> > > check
> > > + * phase.
> > > + *
> > > + * See also:
> > > + * drm_dp_atomic_find_vcpi_slots()
> > > + * drm_dp_mst_atomic_check()
> > > + *
> > > + * Returns:
> > > + * 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 *pos;
> > > + bool found = false;
> > >
> > > 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(pos, &topology_state->vcpis, next) {
> > > + if (pos->port == port) {
> > > + found = true;
> > > + break;
> > > + }
> > > + }
> > > + if (WARN_ON(!found)) {
> > > + DRM_ERROR("no VCPI for [MST PORT:%p] found in mst state %p\n",
> > > + port, &topology_state->base);
> > > + return -EINVAL;
> > > + }
> > > +
> > > + DRM_DEBUG_ATOMIC("[MST PORT:%p] VCPI %d -> 0\n", port, pos->vcpi);
> > > + if (pos->vcpi) {
> > > + /*
> > > + * This should be safe-as the previous state will still hold a
> > > + * reference to this port until we swap states. If it's not,
> > > + * the driver has a bookkeeping error
> > > + */
> > > + if (WARN_ON(drm_dp_put_port(port))) {
> >
> > The usual way to do this (instead of adding a return value to the normal
> > _put function) is something like
> >
> > kref_put(port, function_that_with_just_a_WARNING_DRM_ERROR)
> >
> > avoids the need for patch 2.
> >
> > > + DRM_ERROR("cannot allocate and release VCPI on [MST
> > > PORT:%p] in the same state\n",
> > > + port);
> > > + return -EINVAL;
> > > + }
> > > + pos->vcpi = 0;
> > > + }
> > >
> > > return 0;
> > > }
> > > @@ -3115,15 +3211,45 @@ 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_vcpi_allocation *pos, *vcpi;
> > >
> > > - state = kmemdup(obj->state, sizeof(*state), GFP_KERNEL);
> > > + state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
> > > if (!state)
> > > return NULL;
> > >
> > > __drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
> > >
> > > + INIT_LIST_HEAD(&state->vcpis);
> > > + state->vcpi_allocated = false;
> > > +
> > > + list_for_each_entry(pos, &old_state->vcpis, next) {
> > > + /* Prune leftover freed VCPI allocations */
> > > + if (!pos->vcpi)
> > > + continue;
> > > +
> > > + vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> > > + if (!vcpi)
> > > + goto fail;
> > > +
> > > + /* Take a plain old kref here and don't validate the port, as
> > > + * it's topology might not even exist anymore
> > > + */
> > > + kref_get(&vcpi->port->kref);
> > > + list_add(&vcpi->next, &state->vcpis);
> > > + }
> > > +
> > > return &state->base;
> > > +
> > > +fail:
> > > + list_for_each_entry_safe(pos, vcpi, &state->vcpis, next) {
> > > + drm_dp_put_port(pos->port);
> > > + kfree(pos);
> > > + }
> > > + kfree(state);
> > > +
> > > + return NULL;
> > > }
> > >
> > > static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> > > @@ -3131,14 +3257,116 @@ 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;
> > > +
> > > + list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next) {
> > > + /* We only keep references to ports with non-zero VCPIs */
> > > + if (pos->vcpi)
> > > + drm_dp_put_port(pos->port);
> > > + kfree(pos);
> > > + }
> > >
> > > kfree(mst_state);
> > > }
> > >
> > > -static const struct drm_private_state_funcs mst_state_funcs = {
> > > +static inline int
> > > +drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr
> > > *mgr,
> > > + struct drm_dp_mst_topology_state
> > > *mst_state)
> > > +{
> > > + struct drm_dp_vcpi_allocation *vcpi;
> > > + struct drm_dp_mst_port *port;
> > > + int avail_slots = 63, ret;
> > > +
> > > + /* There's no possible scenario where releasing VCPI or keeping it the
> > > + * same would make the state invalid
> > > + */
> > > + if (!mst_state->vcpi_allocated) {
> >
> > Do we need this? If not I'm always in favour of removing code if it's not
> > needed :-)
> answered by my explanation above ^
If removing this breaks the code then I think it's a bit fragile. And see
above, open to races (yes unlikely ones, but then all of mst is full of
unlikely races it that still seem to happen eventually).
I think it's better if we can remove all these special cases (which should
be possible if we drop the get_validated_port below).
> >
> > > + DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p allocates no VCPI,
> > > check skipped\n",
> > > + mgr, &mst_state->base);
> > > + return 0;
> > > + }
> > > +
> > > + list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> > > + /* Releasing VCPI is always OK-even if the port is gone */
> > > + if (!vcpi->vcpi) {
> > > + DRM_DEBUG_ATOMIC("[MST PORT:%p] releases all VCPI
> > > slots\n",
> > > + vcpi->port);
> > > + continue;
> > > + }
> > > +
> > > + port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> > > + if (!port) {
> > > + DRM_DEBUG_ATOMIC("[MST PORT:%p] is gone but still has
> > > VCPI, cannot add new VCPI\n",
> > > + vcpi->port);
> > > + return -EINVAL;
> > > + }
> >
> > For find_vcpi we've already done this. For unplugged vcpi, we can't do
> > this here I think - otherwise if you enable 2 mst outputs on the same
> > branch, and unplug both, old non-atomic userspace can never ever again
> > disable them because it can't disable both. The check (to skip already
> > deallocated ports) above isn't enough to handle that.
>
> answered by my explanation above ^
> >
> > > +
> > > + DRM_DEBUG_ATOMIC("[MST PORT:%p] requires %d vcpi slots\n",
> > > + vcpi->port, vcpi->vcpi);
> > > +
> > > + avail_slots -= vcpi->vcpi;
> > > + if (avail_slots < 0) {
> > > + DRM_DEBUG_ATOMIC("[MST PORT:%p] not enough VCPI slots
> > > in mst state %p (avail=%d)\n",
> > > + vcpi->port, mst_state,
> > > + avail_slots + vcpi->vcpi);
> > > + ret = -ENOSPC;
> > > + goto port_fail;
> > > + }
> > > +
> > > + drm_dp_put_port(port);
> > > + }
> > > + DRM_DEBUG_ATOMIC("[MST MGR:%p] mst state %p VCPI avail=%d used=%d\n",
> > > + mgr, mst_state, avail_slots,
> > > + 63 - avail_slots);
> > > +
> > > + return 0;
> > > +port_fail:
> > > + drm_dp_put_port(port);
> > > + return ret;
> > > +}
> > > +
> > > +/**
> > > + * 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
> > > + * &drm_mode_config_funcs.atomic_check() callback.
> > > + *
> > > + * See also:
> > > + * drm_dp_atomic_find_vcpi_slots()
> > > + * drm_dp_atomic_release_vcpi_slots()
> > > + *
> > > + * Returns:
> > > + *
> > > + * 0 if the new state is valid, negative error code otherwise.
> > > + */
> > > +int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
> > > +{
> > > + struct drm_dp_mst_topology_mgr *mgr;
> > > + struct drm_dp_mst_topology_state *mst_state;
> > > + int i, ret = 0;
> > > +
> > > + for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
> > > + ret = drm_dp_mst_atomic_check_topology_state(mgr, mst_state);
> > > + if (ret)
> > > + break;
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +EXPORT_SYMBOL(drm_dp_mst_atomic_check);
> > > +
> > > +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
> > > @@ -3216,13 +3444,11 @@ 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 132e978227fb..8e85e04a5948 100644
> > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > @@ -12592,6 +12592,10 @@ static int intel_atomic_check(struct drm_device
> > > *dev,
> > > "[modeset]" : "[fastset]");
> > > }
> > >
> > > + ret = drm_dp_mst_atomic_check(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 4de247ddf05f..be2d1ac7d87d 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > > @@ -41,8 +41,13 @@ static bool intel_dp_mst_compute_config(struct
> > > intel_encoder *encoder,
> > > struct drm_connector *connector = conn_state->connector;
> > > void *port = to_intel_connector(connector)->port;
> > > struct drm_atomic_state *state = pipe_config->base.state;
> > > + struct drm_crtc *crtc = pipe_config->base.crtc;
> > > + struct drm_crtc_state *old_crtc_state =
> > > + drm_atomic_get_old_crtc_state(state, crtc);
> > > + struct drm_crtc_state *new_crtc_state = &pipe_config->base;
> > > int bpp;
> > > - int lane_count, slots = 0;
> > > + int lane_count, slots =
> > > + to_intel_crtc_state(old_crtc_state)->dp_m_n.tu;
> > > const struct drm_display_mode *adjusted_mode = &pipe_config-
> > > >base.adjusted_mode;
> > > int mst_pbn;
> > > bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
> > > @@ -77,8 +82,12 @@ static bool intel_dp_mst_compute_config(struct
> > > intel_encoder *encoder,
> > > mst_pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock, bpp);
> > > pipe_config->pbn = mst_pbn;
> > >
> > > - /* Zombie connectors can't have VCPI slots */
> > > - if (!drm_connector_is_unregistered(connector)) {
> > > + /* Only change VCPI allocation on actual mode changes, to prevent us
> > > + * from trying to allocate VCPI to ports that no longer exist when we
> > > + * may just be trying to disable DPMS on them
> > > + */
> > > + if (new_crtc_state->mode_changed ||
> > > + new_crtc_state->connectors_changed) {
> >
> > Why exactly is this needed? We only call compute_config on the enocoder
> > when enabling an output. Not when disabling one. Similar for the atomic
> > helpers and the various encoder callbacks (you have the same change in the
> > nouveau code). Did this actually blow up while testing?
>
> yes-it looked like we were calling compute_config on simple DPMS on->off
> chnges as well, this ended up making it so we wouldn't try changing the VCPI
> allocation on such commits.
Ah right, we discussed all this when adding the is_unregistered() check.
If we don't change the port lifetime (but only when kfree is called) then
there's no need to change anything here. Allows us to keep the nice
consistency of the is_unregistered() check in driver code.
I should have rewritten this when I realized that you've changed the
lifetime rules in a different way than what I had in mind, as-is my
comment didn't make much sense.
-Daniel
> ACK on all of the other comments here.
> >
> > > slots = drm_dp_atomic_find_vcpi_slots(state,
> > > &intel_dp->mst_mgr,
> > > port,
> > > @@ -107,36 +116,39 @@ static bool intel_dp_mst_compute_config(struct
> > > intel_encoder *encoder,
> > > return true;
> > > }
> > >
> > > -static int intel_dp_mst_atomic_check(struct drm_connector *connector,
> > > - struct drm_connector_state *new_conn_state)
> > > +static int
> > > +intel_dp_mst_atomic_check(struct drm_connector *connector,
> > > + struct drm_connector_state *new_conn_state)
> > > {
> > > + 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;
> > > struct drm_atomic_state *state = new_conn_state->state;
> > > - struct drm_connector_state *old_conn_state;
> > > - struct drm_crtc *old_crtc;
> > > - struct drm_crtc_state *crtc_state;
> > > - int slots, ret = 0;
> > > + struct drm_connector_state *old_conn_state =
> > > + drm_atomic_get_old_connector_state(state, connector);
> > > + struct drm_crtc *old_crtc = old_conn_state->crtc,
> > > + *new_crtc = new_conn_state->crtc;
> > > + struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> > >
> > > - old_conn_state = drm_atomic_get_old_connector_state(state, connector);
> > > - old_crtc = old_conn_state->crtc;
> >
> > Bikeshed: Reworking all the above hides the real changes quite a bit.
> >
> > > if (!old_crtc)
> > > - return ret;
> > > + return 0;
> > >
> > > - 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;
> > > + old_crtc_state = drm_atomic_get_old_crtc_state(state, old_crtc);
> > > + if (!old_crtc_state ||
> >
> > !old_crtc_state would be a framework bug. Just remove that check.
> >
> > > + !to_intel_crtc_state(old_crtc_state)->dp_m_n.tu)
> > > + return 0;
> >
> > Hm, why do we need this? Having a DP port previously enabled with a 0 tu
> > sounds like a pretty big driver bug.
> > >
> > > - old_encoder = old_conn_state->best_encoder;
> > > - mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> > > + /* If we switched CRTCs, clear the previous one's allocation */
> > > + new_crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> > > + if (new_crtc_state->connectors_changed && !new_crtc_state->enable)
> > > + to_intel_crtc_state(new_crtc_state)->dp_m_n.tu = 0;
> >
> > No idea why we need to clear this here? Shouldn't we just clear this
> > unconditionally if we release the allocation.
> >
> > Also naming convention, I'd call this old_crtc_new_state, and maybe
> > old_crtc_old_state. To make it clear these are the old/new states for
> > old_crtc. Instead of old/new state for the new crtc.
> >
> > >
> > > - 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;
> > > - }
> > > - return ret;
> > > + if (new_crtc)
> > > + return 0;
> >
> > Not sure why we shouldn't release this? If we handle this in helpers, it
> > would remove piles of special casing code here I think. Plus remove
> > special code in the hlpers.
> >
> >
> > > +
> > > + return drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> > > }
> > >
> > > static void intel_mst_disable_dp(struct intel_encoder *encoder,
> > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > b/include/drm/drm_dp_mst_helper.h
> > > index 3faceb66f5cb..2392e12b6bce 100644
> > > --- a/include/drm/drm_dp_mst_helper.h
> > > +++ b/include/drm/drm_dp_mst_helper.h
> > > @@ -406,9 +406,16 @@ 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 {
> >
> > I think a comment here that this pointer holds a full reference (even past
> > when the connector is unplugged) would be good. Otherwise the loop in
> > release_vcpi would be buggy.
> >
> > > + 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;
> > > + u8 vcpi_allocated;
> > > struct drm_dp_mst_topology_mgr *mgr;
> > > };
> > >
> > > @@ -619,14 +626,17 @@ void drm_dp_mst_topology_mgr_suspend(struct
> > > drm_dp_mst_topology_mgr *mgr);
> > > int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr);
> > > struct drm_dp_mst_topology_state
> > > *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
> > > struct
> > > drm_dp_mst_topology_mgr *mgr);
> > > -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);
> > > -int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> > > - struct drm_dp_mst_topology_mgr *mgr,
> > > - int slots);
> > > +int __must_check
> > > +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);
> > > +int __must_check
> > > +drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> > > + struct drm_dp_mst_topology_mgr *mgr,
> > > + 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);
> > > +int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
> > >
> > > extern const struct drm_private_state_funcs
> > > drm_dp_mst_topology_state_funcs;
> > >
> > > --
> > > 2.19.1
> > >
> --
> Cheers,
> Lyude Paul
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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