On Tue, 2023-02-07 at 14:11 +0200, Imre Deak wrote:
> On Mon, Feb 06, 2023 at 07:42:32PM -0500, Lyude Paul wrote:
> > On Wed, 2023-02-01 at 17:04 +0200, Imre Deak wrote:
> > >
> > > Yes, this patch should have no functional change, so please check what
> > > would apply to other drivers as well.
> > >
> > > Could you also check Ville's comment about storing start_slot elsewhere
> > > than the atomic state (leaving only time_slots there). I wonder if that
> > > would work, at least it would simplify things I think.
> >
> > Ideally it'd be nice if we could have all this info in the atomic commit, but
> > yeah - you're not the first person to find this a bit confusing. FWIW though,
> > the way we store start_slot right now is intended to follow the same kind of
> > behavior we have with atomic CRTC commit dependencies, I think I also made it
> > that way so all of the state would be in a single place but there's no hard
> > requirement for it.
>
> As I understood the atomic state should be precomputed during atomic
> check and not changed later during the commit phase. In case of
> start_slot this would mean knowing in advance the actual (driver
> specific) disabling / enabling sequence of the payloads, not sure how
> feasible it is to figure that out. start_slot also changes dynamically
It isn't feasible afaict, which was the main motivation for having the strange
update procedure - this is pretty much something that needs to be determined
at commit time.
> as each payload is disabled, so these intermediate versions of the field
> would need to be tracked somehow separately from the final (precomputed)
> versions.
FWIW, the current way this works is that we call
drm_dp_mst_atomic_wait_for_dependencies() in order to ensure that no one's
currently writing to the start_slot field (remember, at this point we may not
have atomic locks held anymore). Then at that point, start_slot in the new
atomic state should hold the current in-hw start_slot value. start_slot isn't
actually set to the new starting slot until drm_dp_add_payload_part1(). That
of course as you pointed out, doesn't help us unless we read all of the
start_slot values before we start changing payloads - since disabling payloads
inevitably changes the start slot of payloads that come afterwards.
I'll admit I'm a bit surprised this logic was wrong - if I recall the whole
reason I assumed this was OK when writing this code was that since we're
updating one payload at a time, ACT, repeat, that the start slots of each
payload in hardware _would_ actually change in the same way we modify them in
helpers. e.g., my expectation was if we had a bunch of payloads like this:
Payload #1: 15 slots, start_slot=0
Payload #2: 15 slots, start_slot=15
Payload #3: 15 slots, start_slot=30
And then disabled say, payload #1, that immediately after we get the ACT that
the payload table in hardware would look like this:
Payload #2: 15 slots, start_slot=0
Payload #3: 15 slots, start_slot=15
But it sounds like it actually would look like this in the real world?
Payload #2: 15 slots, start_slot=15
Payload #3: 15 slots, start_slot=30
So I'm curious, is there something I missed here? At what point does the MST
hub at the other end decide that it's time to move the start slots back? (keep
in mind, the MST specification does explicitly mention that there should never
be holes in the payload table - so something has to be shifting the payloads
back).
>
> > So if you guys think it'd be better design-wise to store this something else,
> > I've got no strong feelings either way
> > >
> > > > For 0-2:
> > > >
> > > > Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>
> > >
> > > Thanks.
> > >
> > > >
> > > > >
> > > > > Cc: Lyude Paul <lyude@xxxxxxxxxx>
> > > > > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > > > > Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
> > > > > Cc: Karol Herbst <kherbst@xxxxxxxxxx>
> > > > > Cc: Harry Wentland <harry.wentland@xxxxxxx>
> > > > > Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> > > > > Cc: Wayne Lin <Wayne.Lin@xxxxxxx>
> > > > > Cc: stable@xxxxxxxxxxxxxxx # 6.1
> > > > > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > > > > Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > > > > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> > > > > ---
> > > > > .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 2 +-
> > > > > drivers/gpu/drm/display/drm_dp_mst_topology.c | 26 ++++++++++---------
> > > > > drivers/gpu/drm/i915/display/intel_dp_mst.c | 4 ++-
> > > > > drivers/gpu/drm/nouveau/dispnv50/disp.c | 2 +-
> > > > > include/drm/display/drm_dp_mst_helper.h | 3 ++-
> > > > > 5 files changed, 21 insertions(+), 16 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> > > > > index a50319fc42b11..180d3893b68da 100644
> > > > > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> > > > > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> > > > > @@ -208,7 +208,7 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
> > > > > if (enable)
> > > > > drm_dp_add_payload_part1(mst_mgr, mst_state, payload);
> > > > > else
> > > > > - drm_dp_remove_payload(mst_mgr, mst_state, payload);
> > > > > + drm_dp_remove_payload(mst_mgr, mst_state, payload, payload);
> > > > >
> > > > > /* mst_mgr->->payloads are VC payload notify MST branch using DPCD or
> > > > > * AUX message. The sequence is slot 1-63 allocated sequence for each
> > > > > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > index 847c10aa2098c..1990ff5dc7ddd 100644
> > > > > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > @@ -3342,7 +3342,8 @@ EXPORT_SYMBOL(drm_dp_add_payload_part1);
> > > > > * drm_dp_remove_payload() - Remove an MST payload
> > > > > * @mgr: Manager to use.
> > > > > * @mst_state: The MST atomic state
> > > > > - * @payload: The payload to write
> > > > > + * @old_payload: The payload with its old state
> > > > > + * @new_payload: The payload to write
> > > > > *
> > > > > * Removes a payload from an MST topology if it was successfully assigned a start slot. Also updates
> > > > > * the starting time slots of all other payloads which would have been shifted towards the start of
> > > > > @@ -3350,36 +3351,37 @@ EXPORT_SYMBOL(drm_dp_add_payload_part1);
> > > > > */
> > > > > void drm_dp_remove_payload(struct drm_dp_mst_topology_mgr *mgr,
> > > > > struct drm_dp_mst_topology_state *mst_state,
> > > > > - struct drm_dp_mst_atomic_payload *payload)
> > > > > + const struct drm_dp_mst_atomic_payload *old_payload,
> > > > > + struct drm_dp_mst_atomic_payload *new_payload)
> > > > > {
> > > > > struct drm_dp_mst_atomic_payload *pos;
> > > > > bool send_remove = false;
> > > > >
> > > > > /* We failed to make the payload, so nothing to do */
> > > > > - if (payload->vc_start_slot == -1)
> > > > > + if (new_payload->vc_start_slot == -1)
> > > > > return;
> > > > >
> > > > > mutex_lock(&mgr->lock);
> > > > > - send_remove = drm_dp_mst_port_downstream_of_branch(payload->port, mgr->mst_primary);
> > > > > + send_remove = drm_dp_mst_port_downstream_of_branch(new_payload->port, mgr->mst_primary);
> > > > > mutex_unlock(&mgr->lock);
> > > > >
> > > > > if (send_remove)
> > > > > - drm_dp_destroy_payload_step1(mgr, mst_state, payload);
> > > > > + drm_dp_destroy_payload_step1(mgr, mst_state, new_payload);
> > > > > else
> > > > > drm_dbg_kms(mgr->dev, "Payload for VCPI %d not in topology, not sending remove\n",
> > > > > - payload->vcpi);
> > > > > + new_payload->vcpi);
> > > > >
> > > > > list_for_each_entry(pos, &mst_state->payloads, next) {
> > > > > - if (pos != payload && pos->vc_start_slot > payload->vc_start_slot)
> > > > > - pos->vc_start_slot -= payload->time_slots;
> > > > > + if (pos != new_payload && pos->vc_start_slot > new_payload->vc_start_slot)
> > > > > + pos->vc_start_slot -= old_payload->time_slots;
> > > > > }
> > > > > - payload->vc_start_slot = -1;
> > > > > + new_payload->vc_start_slot = -1;
> > > > >
> > > > > mgr->payload_count--;
> > > > > - mgr->next_start_slot -= payload->time_slots;
> > > > > + mgr->next_start_slot -= old_payload->time_slots;
> > > > >
> > > > > - if (payload->delete)
> > > > > - drm_dp_mst_put_port_malloc(payload->port);
> > > > > + if (new_payload->delete)
> > > > > + drm_dp_mst_put_port_malloc(new_payload->port);
> > > > > }
> > > > > EXPORT_SYMBOL(drm_dp_remove_payload);
> > > > >
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > > > index f3cb12dcfe0a7..dc4e5ff1dbb31 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > > > @@ -526,6 +526,8 @@ static void intel_mst_disable_dp(struct intel_atomic_state *state,
> > > > > to_intel_connector(old_conn_state->connector);
> > > > > struct drm_dp_mst_topology_state *mst_state =
> > > > > drm_atomic_get_mst_topology_state(&state->base, &intel_dp->mst_mgr);
> > > > > + struct drm_dp_mst_atomic_payload *payload =
> > > > > + drm_atomic_get_mst_payload_state(mst_state, connector->port);
> > > > > struct drm_i915_private *i915 = to_i915(connector->base.dev);
> > > > >
> > > > > drm_dbg_kms(&i915->drm, "active links %d\n",
> > > > > @@ -534,7 +536,7 @@ static void intel_mst_disable_dp(struct intel_atomic_state *state,
> > > > > intel_hdcp_disable(intel_mst->connector);
> > > > >
> > > > > drm_dp_remove_payload(&intel_dp->mst_mgr, mst_state,
> > > > > - drm_atomic_get_mst_payload_state(mst_state, connector->port));
> > > > > + payload, payload);
> > > > >
> > > > > intel_audio_codec_disable(encoder, old_crtc_state, old_conn_state);
> > > > > }
> > > > > diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > > > > index edcb2529b4025..ed9d374147b8d 100644
> > > > > --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > > > > +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > > > > @@ -885,7 +885,7 @@ nv50_msto_prepare(struct drm_atomic_state *state,
> > > > >
> > > > > // TODO: Figure out if we want to do a better job of handling VCPI allocation failures here?
> > > > > if (msto->disabled) {
> > > > > - drm_dp_remove_payload(mgr, mst_state, payload);
> > > > > + drm_dp_remove_payload(mgr, mst_state, payload, payload);
> > > > >
> > > > > nvif_outp_dp_mst_vcpi(&mstm->outp->outp, msto->head->base.index, 0, 0, 0, 0);
> > > > > } else {
> > > > > diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
> > > > > index 41fd8352ab656..f5eb9aa152b14 100644
> > > > > --- a/include/drm/display/drm_dp_mst_helper.h
> > > > > +++ b/include/drm/display/drm_dp_mst_helper.h
> > > > > @@ -841,7 +841,8 @@ int drm_dp_add_payload_part2(struct drm_dp_mst_topology_mgr *mgr,
> > > > > struct drm_dp_mst_atomic_payload *payload);
> > > > > void drm_dp_remove_payload(struct drm_dp_mst_topology_mgr *mgr,
> > > > > struct drm_dp_mst_topology_state *mst_state,
> > > > > - struct drm_dp_mst_atomic_payload *payload);
> > > > > + const struct drm_dp_mst_atomic_payload *old_payload,
> > > > > + struct drm_dp_mst_atomic_payload *new_payload);
> > > > >
> > > > > int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr);
> > > > >
> > > >
> > > > --
> > > > Cheers,
> > > > Lyude Paul (she/her)
> > > > Software Engineer at Red Hat
> > > >
> > >
> >
> > --
> > Cheers,
> > Lyude Paul (she/her)
> > Software Engineer at Red Hat
> >
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
