[PATCH] drm/i915/mst: add beginnings of DP MST documentation

[Jani Nikula]

On Wed, 04 Dec 2024, Imre Deak <imre.deak at intel.com> wrote:
> On Mon, Nov 25, 2024 at 05:19:33PM +0200, Jani Nikula wrote:
>> Add a little bit of documentation around DP MST. This is nowhere near
>> complete nor does it have enough detail. But it's better than nothing,
>> and hopefully gives people a basic grasp of what's going on.
>> 
>> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>
> Reviewed-by: Imre Deak <imre.deak at intel.com>

Thanks, pushed to drm-intel-next. This being a pure comment change, I
exceptionally chose to ignore the CI results.

BR,
Jani.

>
>> ---
>>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 32 +++++++++++++++++++++
>>  1 file changed, 32 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> index c59c2c14679c..a9ce8b3a7ff5 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> @@ -53,6 +53,38 @@
>>  #include "intel_vdsc.h"
>>  #include "skl_scaler.h"
>>  
>> +/*
>> + * DP MST (DisplayPort Multi-Stream Transport)
>> + *
>> + * MST support on the source depends on the platform and port. DP initialization
>> + * sets up MST for each MST capable encoder. This will become the primary
>> + * encoder for the port.
>> + *
>> + * MST initialization of each primary encoder creates MST stream encoders, one
>> + * per pipe, and initializes the MST topology manager. The MST stream encoders
>> + * are sometimes called "fake encoders", because they're virtual, not
>> + * physical. Thus there are (number of MST capable ports) x (number of pipes)
>> + * MST stream encoders in total.
>> + *
>> + * Decision to use MST for a sink happens at detect on the connector attached to
>> + * the primary encoder, and this will not change while the sink is connected. We
>> + * always use MST when possible, including for SST sinks with sideband messaging
>> + * support.
>> + *
>> + * The connectors for the MST streams are added and removed dynamically by the
>> + * topology manager. Their connection status is also determined by the topology
>> + * manager.
>> + *
>> + * On hardware, each transcoder may be associated with a single DDI
>> + * port. Multiple transcoders may be associated with the same DDI port only if
>> + * the port is in MST mode.
>> + *
>> + * On TGL+, all the transcoders streaming on the same DDI port will indicate a
>> + * primary transcoder; the TGL_DP_TP_CTL and TGL_DP_TP_STATUS registers are
>> + * relevant only on the primary transcoder. Prior to that, they are port
>> + * registers.
>> + */
>> +
>>  /* From fake MST stream encoder to primary encoder */
>>  static struct intel_encoder *to_primary_encoder(struct intel_encoder *encoder)
>>  {
>> -- 
>> 2.39.5
>> 

-- 
Jani Nikula, Intel