drm/display/dp_mst: Move all payload info into the atomic state
Now that we've finally gotten rid of the non-atomic MST users leftover in the kernel, we can finally get rid of all of the legacy payload code we have and move as much as possible into the MST atomic state structs. The main purpose of this is to make the MST code a lot less confusing to work on, as there's a lot of duplicated logic that doesn't really need to be here. As well, this should make introducing features like fallback link retraining and DSC support far easier. Since the old payload code was pretty gnarly and there's a Lot of changes here, I expect this might be a bit difficult to review. So to make things as easy as possible for reviewers, I'll sum up how both the old and new code worked here (it took me a while to figure this out too!). The old MST code basically worked by maintaining two different payload tables - proposed_vcpis, and payloads. proposed_vcpis would hold the modified payload we wanted to push to the topology, while payloads held the payload table that was currently programmed in hardware. Modifications to proposed_vcpis would be handled through drm_dp_allocate_vcpi(), drm_dp_mst_deallocate_vcpi(), and drm_dp_mst_reset_vcpi_slots(). Then, they would be pushed via drm_dp_mst_update_payload_step1() and drm_dp_mst_update_payload_step2(). Furthermore, it's important to note how adding and removing VC payloads actually worked with drm_dp_mst_update_payload_step1(). When a VC payload is removed from the VC table, all VC payloads which come after the removed VC payload's slots must have their time slots shifted towards the start of the table. The old code handles this by looping through the entire payload table and recomputing the start slot for every payload in the topology from scratch. While very much overkill, this ends up doing the right thing because we always order the VCPIs for payloads from first to last starting timeslot. It's important to also note that drm_dp_mst_update_payload_step2() isn't actually limited to updating a single payload - the driver can use it to queue up multiple payload changes so that as many of them can be sent as possible before waiting for the ACT. This is -technically- not against spec, but as Wayne Lin has pointed out it's not consistently implemented correctly in hubs - so it might as well be. drm_dp_mst_update_payload_step2() is pretty self explanatory and basically the same between the old and new code, save for the fact we don't have a second step for deleting payloads anymore -and thus rename it to drm_dp_mst_add_payload_step2(). The new payload code stores all of the current payload info within the MST atomic state and computes as much of the state as possible ahead of time. This has the one exception of the starting timeslots for payloads, which can't be determined at atomic check time since the starting time slots will vary depending on what order CRTCs are enabled in the atomic state - which varies from driver to driver. These are still stored in the atomic MST state, but are only copied from the old MST state during atomic commit time. Likewise, this is when new start slots are determined. Adding/removing payloads now works much more closely to how things are described in the spec. When we delete a payload, we loop through the current list of payloads and update the start slots for any payloads whose time slots came after the payload we just deleted. Determining the starting time slots for new payloads being added is done by simply keeping track of where the end of the VC table is in drm_dp_mst_topology_mgr->next_start_slot. Additionally, it's worth noting that we no longer have a single update_payload() function. Instead, we now have drm_dp_mst_add_payload_step1|2() and drm_dp_mst_remove_payload(). As such, it's now left it up to the driver to figure out when to add or remove payloads. The driver already knows when it's disabling/enabling CRTCs, so it also already knows when payloads should be added or removed. Changes since v1: * Refactor around all of the completely dead code changes that are happening in amdgpu for some reason when they really shouldn't even be there in the first place… :\ * Remove mention of sending one ACT per series of payload updates. As Wayne Lin pointed out, there are apparently hubs on the market that don't work correctly with this scheme and require a separate ACT per payload update. * Fix accidental drop of mst_mgr.lock - Wayne Lin * Remove mentions of allowing multiple ACT updates per payload change, mention that this is a result of vendors not consistently supporting this part of the spec and requiring a unique ACT for each payload change. * Get rid of reference to drm_dp_mst_port in DC - turns out I just got myself confused by DC and we don't actually need this. Changes since v2: * Get rid of fix for not sending payload deallocations if ddps=0 and just go back to wayne's fix Signed-off-by:Lyude Paul <lyude@redhat.com> Cc: Wayne Lin <Wayne.Lin@amd.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Fangzhi Zuo <Jerry.Zuo@amd.com> Cc: Jani Nikula <jani.nikula@intel.com> Cc: Imre Deak <imre.deak@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Sean Paul <sean@poorly.run> Acked-by:
Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20220817193847.557945-18-lyude@redhat.com
Showing
This diff is collapsed.
This diff is collapsed.
This diff is collapsed.
Please register or sign in to comment