Re: [PATCH] drm: Update MST First Link Slot Information Based on Encoding Format

[Bhawanpreet Lakha <Bhawanpreet.lakha@xxxxxxx>]

I understand the mst_state argument its just that most of the mst 
functions are using mst_mgr/port structs and there is no easy way to 
extract the mst_state using mgr/port in these places 
(drm_dp_update_payload_part1, drm_dp_mst_allocate_vcpi, drm_dp_init_vcpi 
etc) where we need the slot info.

So either we need to keep a copy of the slots in the mgr because that's 
what most of the code is using right now or pass around the atomic state 
to get the mgr->state mapping. (I don't have much experience with the 
mst code so maybe I am missing some key detail here?)


Thanks,

Bhawan


On 2021-10-15 4:41 p.m., Lyude Paul wrote:
> [more snip]
>
> On Fri, 2021-10-15 at 15:43 -0400, Bhawanpreet Lakha wrote:
> > Thanks for the response,
> >
> > That function is per port so not sure how that will work. Also we only
> > need to check this inside drm_dp_mst_atomic_check_vcpi_alloc_limit(),
> > which doesn't have a state.
> >
> > We could add the slots(or some DP version indicator) inside the
> > drm_connector, and add a parameter to
> > drm_dp_mst_atomic_check_vcpi_alloc_limit(int slots)? and call it with
> > this info via drm_dp_mst_atomic_check() and then update the mgr->slot in
> > commit.
> TBH - I think we can actually just get away with having all of this info in
> drm_dp_mst_topology_state
>
> > Bhawan
> >
> > > >                   ret = drm_dp_mst_atomic_check_mstb_bw_limit(mgr-
> > > > > mst_primary,
> > > >                                                               mst_state);
> > > >                   mutex_unlock(&mgr->lock);
> > > > @@ -5527,11 +5543,16 @@ int drm_dp_mst_topology_mgr_init(struct
> > > > drm_dp_mst_topology_mgr *mgr,
> > > >           if (!mgr->proposed_vcpis)
> > > >                   return -ENOMEM;
> > > >           set_bit(0, &mgr->payload_mask);
> > > > +       mgr->total_avail_slots = 63;
> > > > +       mgr->start_slot = 1;
> > > >    
> > > >           mst_state = kzalloc(sizeof(*mst_state), GFP_KERNEL);
> > > >           if (mst_state == NULL)
> > > >                   return -ENOMEM;
> > > >    
> > > > +       mst_state->total_avail_slots = 63;
> > > > +       mst_state->start_slot = 1;
> > > > +
> > > >           mst_state->mgr = mgr;
> > > >           INIT_LIST_HEAD(&mst_state->vcpis);
> > > >    
> > > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > > b/include/drm/drm_dp_mst_helper.h
> > > > index ddb9231d0309..f8152dfb34ed 100644
> > > > --- a/include/drm/drm_dp_mst_helper.h
> > > > +++ b/include/drm/drm_dp_mst_helper.h
> > > > @@ -554,6 +554,8 @@ struct drm_dp_mst_topology_state {
> > > >           struct drm_private_state base;
> > > >           struct list_head vcpis;
> > > >           struct drm_dp_mst_topology_mgr *mgr;
> > > > +       u8 total_avail_slots;
> > > > +       u8 start_slot;
> > > >    };
> > > >    
> > > >    #define to_dp_mst_topology_mgr(x) container_of(x, struct
> > > > drm_dp_mst_topology_mgr, base)
> > > > @@ -661,6 +663,16 @@ struct drm_dp_mst_topology_mgr {
> > > >            */
> > > >           int pbn_div;
> > > >    
> > > > +       /**
> > > > +        * @total_avail_slots: 63 for 8b/10b, 64 for 128/132b
> > > > +        */
> > > > +       u8 total_avail_slots;
> > > > +
> > > > +       /**
> > > > +        * @start_slot: 1 for 8b/10b, 0 for 128/132b
> > > > +        */
> > > > +       u8 start_slot;
> > > > +
> > > >           /**
> > > >            * @funcs: Atomic helper callbacks
> > > >            */
> > > > @@ -806,6 +818,7 @@ int drm_dp_mst_get_vcpi_slots(struct
> > > > drm_dp_mst_topology_mgr *mgr, struct drm_dp
> > > >    
> > > >    void drm_dp_mst_reset_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr,
> > > > struct drm_dp_mst_port *port);
> > > >    
> > > > +void drm_dp_mst_update_coding_cap(struct drm_dp_mst_topology_state
> > > > *mst_state, uint8_t link_coding_cap);
> > > >    
> > > >    void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
> > > >                                   struct drm_dp_mst_port *port);