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

[Bhawanpreet Lakha <Bhawanpreet.lakha@amd.com>]

On 2021-10-13 6:25 p.m., Lyude Paul wrote:
> Some comments below (also, sorry again for the mixup on the last review!)
>
> On Tue, 2021-10-12 at 17:58 -0400, Bhawanpreet Lakha wrote:
>> 8b/10b encoding format requires to reserve the first slot for
>> recording metadata. Real data transmission starts from the second slot,
>> with a total of available 63 slots available.
>>
>> In 128b/132b encoding format, metadata is transmitted separately
>> in LLCP packet before MTP. Real data transmission starts from
>> the first slot, with a total of 64 slots available.
>>
>> v2:
>> * Remove get_mst_link_encoding_cap
>> * Move total/start slots to mst_state, and copy it to mst_mgr in
>> atomic_check
>>
>> Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
>> Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
>> ---
>>   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 28 +++++++++++++++
>>   drivers/gpu/drm/drm_dp_mst_topology.c         | 35 +++++++++++++++----
>>   include/drm/drm_dp_mst_helper.h               | 13 +++++++
>>   3 files changed, 69 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> index 5020f2d36fe1..4ad50eb0091a 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> @@ -10612,6 +10612,8 @@ static int amdgpu_dm_atomic_check(struct drm_device
>> *dev,
>>   #if defined(CONFIG_DRM_AMD_DC_DCN)
>>          struct dsc_mst_fairness_vars vars[MAX_PIPES];
>>   #endif
>> +       struct drm_dp_mst_topology_state *mst_state;
>> +       struct drm_dp_mst_topology_mgr *mgr;
>>   
>>          trace_amdgpu_dm_atomic_check_begin(state);
>>   
>> @@ -10819,6 +10821,32 @@ static int amdgpu_dm_atomic_check(struct drm_device
>> *dev,
>>                  lock_and_validation_needed = true;
>>          }
>>   
>> +#if defined(CONFIG_DRM_AMD_DC_DCN)
>> +       for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
>> +               struct amdgpu_dm_connector *aconnector;
>> +               struct drm_connector *connector;
>> +               struct drm_connector_list_iter iter;
>> +               u8 link_coding_cap;
>> +
>> +               if (!mgr->mst_state )
>> +                       continue;
> extraneous space
>
>> +
>> +               drm_connector_list_iter_begin(dev, &iter);
>> +               drm_for_each_connector_iter(connector, &iter) {
>> +                       int id = connector->index;
>> +
>> +                       if (id == mst_state->mgr->conn_base_id) {
>> +                               aconnector =
>> to_amdgpu_dm_connector(connector);
>> +                               link_coding_cap =
>> dc_link_dp_mst_decide_link_encoding_format(aconnector->dc_link);
>> +                               drm_dp_mst_update_coding_cap(mst_state,
>> link_coding_cap);
>> +
>> +                               break;
>> +                       }
>> +               }
>> +               drm_connector_list_iter_end(&iter);
>> +
>> +       }
>> +#endif
>>          /**
>>           * Streams and planes are reset when there are changes that affect
>>           * bandwidth. Anything that affects bandwidth needs to go through
>> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
>> b/drivers/gpu/drm/drm_dp_mst_topology.c
>> index ad0795afc21c..fb5c47c4cb2e 100644
>> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
>> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>> @@ -3368,7 +3368,7 @@ int drm_dp_update_payload_part1(struct
>> drm_dp_mst_topology_mgr *mgr)
>>          struct drm_dp_payload req_payload;
>>          struct drm_dp_mst_port *port;
>>          int i, j;
>> -       int cur_slots = 1;
>> +       int cur_slots = mgr->start_slot;
>>          bool skip;
>>   
>>          mutex_lock(&mgr->payload_lock);
>> @@ -4321,7 +4321,7 @@ int drm_dp_find_vcpi_slots(struct
>> drm_dp_mst_topology_mgr *mgr,
>>          num_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
>>   
>>          /* max. time slots - one slot for MTP header */
>> -       if (num_slots > 63)
>> +       if (num_slots > mgr->total_avail_slots)
>>                  return -ENOSPC;
> For reasons I will explain a little further in this email, we might want to
> drop this…
>
>>          return num_slots;
>>   }
>> @@ -4333,7 +4333,7 @@ static int drm_dp_init_vcpi(struct
>> drm_dp_mst_topology_mgr *mgr,
>>          int ret;
>>   
>>          /* max. time slots - one slot for MTP header */
>> -       if (slots > 63)
>> +       if (slots > mgr->total_avail_slots)
> …and this
>
>>                  return -ENOSPC;
>>   
>>          vcpi->pbn = pbn;
>> @@ -4507,6 +4507,18 @@ int drm_dp_atomic_release_vcpi_slots(struct
>> drm_atomic_state *state,
>>   }
>>   EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
>>   
>> +void drm_dp_mst_update_coding_cap(struct drm_dp_mst_topology_state
>> *mst_state, uint8_t link_coding_cap)
> Need some kdocs here
>
>> +{
>> +       if (link_coding_cap == DP_CAP_ANSI_128B132B) {
>> +               mst_state->total_avail_slots = 64;
>> +               mst_state->start_slot = 0;
>> +       }
>> +
>> +       DRM_DEBUG_KMS("%s coding format on mgr 0x%p\n",
>> +                       (link_coding_cap == DP_CAP_ANSI_128B132B) ?
>> "128b/132b":"8b/10b", mst_state->mgr);
> need to fix indenting here, and wrap this to 100 chars
>
>> +}
>> +EXPORT_SYMBOL(drm_dp_mst_update_coding_cap);
>> +
>>   /**
>>    * drm_dp_mst_allocate_vcpi() - Allocate a virtual channel
>>    * @mgr: manager for this port
>> @@ -4538,8 +4550,8 @@ bool drm_dp_mst_allocate_vcpi(struct
>> drm_dp_mst_topology_mgr *mgr,
>>   
>>          ret = drm_dp_init_vcpi(mgr, &port->vcpi, pbn, slots);
>>          if (ret) {
>> -               drm_dbg_kms(mgr->dev, "failed to init vcpi slots=%d max=63
>> ret=%d\n",
>> -                           DIV_ROUND_UP(pbn, mgr->pbn_div), ret);
>> +               drm_dbg_kms(mgr->dev, "failed to init vcpi slots=%d max=%d
>> ret=%d\n",
>> +                           DIV_ROUND_UP(pbn, mgr->pbn_div), mgr-
>>> total_avail_slots, ret);
>>                  drm_dp_mst_topology_put_port(port);
>>                  goto out;
>>          }
>> @@ -5226,7 +5238,7 @@ drm_dp_mst_atomic_check_vcpi_alloc_limit(struct
>> drm_dp_mst_topology_mgr *mgr,
>>                                           struct drm_dp_mst_topology_state
>> *mst_state)
>>   {
>>          struct drm_dp_vcpi_allocation *vcpi;
>> -       int avail_slots = 63, payload_count = 0;
>> +       int avail_slots = mgr->total_avail_slots, payload_count = 0;
>>   
>>          list_for_each_entry(vcpi, &mst_state->vcpis, next) {
>>                  /* Releasing VCPI is always OK-even if the port is gone */
>> @@ -5255,7 +5267,7 @@ drm_dp_mst_atomic_check_vcpi_alloc_limit(struct
>> drm_dp_mst_topology_mgr *mgr,
>>                  }
>>          }
>>          drm_dbg_atomic(mgr->dev, "[MST MGR:%p] mst state %p VCPI avail=%d
>> used=%d\n",
>> -                      mgr, mst_state, avail_slots, 63 - avail_slots);
>> +                      mgr, mst_state, avail_slots, mgr->total_avail_slots -
>> avail_slots);
>>   
>>          return 0;
>>   }
>> @@ -5421,6 +5433,10 @@ int drm_dp_mst_atomic_check(struct drm_atomic_state
>> *state)
>>                          break;
>>   
>>                  mutex_lock(&mgr->lock);
>> +
>> +               mgr->start_slot = mst_state->start_slot;
>> +               mgr->total_avail_slots = mst_state->total_avail_slots;
>> +
> this isn't correct - atomic checks aren't allowed to mutate anything besides
> the atomic state structure that we're checking since we don't know whether or
> not the display state is going to be committed when checking it. If we're
> storing state in mgr, that state needs to be written to mgr during the atomic
> commit instead of the atomic check.
>
> ...but, coming back to this MST code after being gone for a while, I think it
> might be time for us to stop worrying about the non-atomic state. Especially
> since there's only one driver using it; the legacy radeon.ko; and right now
> the plan is either to just drop MST support on radeon.ko or move the MST code
> it uses into radeon.ko.Which brings me to say - I think we can drop some of
> the hunks I mentioned above (e.g. the changes to drm_dp_init_vcpi and
> drm_dp_find_vcpi_slots I mentioned above). We can then just update the kdocs
> for these functions in a separate patch to clarify that now in addition to
> being deprecated, these functions are just broken and will eventually be
> removed.
>
> So - doing that allows us to get rid of mgr->total_avail_slots and mgr-
>> start_slot entirely, just set the slot info in the atomic state during atomic
> check, and then just rely on the atomic state for
> drm_dp_atomic_find_vcpi_slots() and friends. Which seems much simpler to me,
> does this sound alrght with you?
>
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.


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);