[Intel-gfx] [PATCH v6 3/6] drm/dp_mst: Start tracking per-port VCPI allocations
Lyude Paul
lyude at redhat.com
Mon Nov 26 21:36:46 UTC 2018
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 at redhat.com>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > ---
> > 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.
>
> 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 ^
>
> > + 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.
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
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