Re: [PATCH 02/16] drm/i915/dp_mst: Use VRR Timing generator for DP MST for fixed_rr

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Mar 24, 2025 at 07:02:34PM +0530, Ankit Nautiyal wrote:
> Currently the variable timings are supported only for DP and eDP and not
> for DP MST. Call intel_vrr_compute_config() for MST which will configure
> fixed refresh rate timings irrespective of whether VRR is supported or
> not. Since vrr_capable still doesn't have support for DP MST this will be
> just treated as non VRR case and vrr.vmin/vmax/flipline will be all set
> to adjusted_mode->crtc_vtotal.
> 
> This will help to move away from the legacy timing generator and
> always use VRR timing generator by default.
> 
> With this change, we need to exclude MST in intel_vrr_is_capable for
> now, to avoid having LRR with MST.
> 
> v2: Exclude MST in intel_vrr_is_capable() for now. (Ville)
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 3 +++
>  drivers/gpu/drm/i915/display/intel_vrr.c    | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 02f95108c637..bd47cf127b4c 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -52,6 +52,7 @@
>  #include "intel_pfit.h"
>  #include "intel_psr.h"
>  #include "intel_vdsc.h"
> +#include "intel_vrr.h"
>  #include "skl_scaler.h"
>  
>  /*
> @@ -710,6 +711,8 @@ static int mst_stream_compute_config(struct intel_encoder *encoder,
>  		pipe_config->lane_lat_optim_mask =
>  			bxt_dpio_phy_calc_lane_lat_optim_mask(pipe_config->lane_count);
>  
> +	intel_vrr_compute_config(pipe_config, conn_state);
> +
>  	intel_dp_audio_compute_config(encoder, pipe_config, conn_state);
>  
>  	intel_ddi_compute_min_voltage_level(pipe_config);
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> index 6bdcdfed4b9b..c682c487eb25 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> @@ -32,6 +32,8 @@ bool intel_vrr_is_capable(struct intel_connector *connector)
>  			return false;
>  		fallthrough;
>  	case DRM_MODE_CONNECTOR_DisplayPort:
> +		if (connector->mst.dp)
> +			return false;

The DP spec is pretty vague about this, but it looks to me like it's
saying that the last MST branch device must support the "ignore MSA"
bit in order to support adaptive sync. I guess we might need to do that
stuff via remote DPCD. Or perhaps in the worst case we'd have iterate
through the whole MST chain.

Looks like there's at least this MST hub that claims adaptive sync
support:
https://club-3d.com/en/detail/2486/usb_type_c_3.2_gen_1_multi_stream_transport_(mst)hub_displayport1.4_triple_monitor/
We should probably get one and see if we can get this working.

In the meantime
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  		intel_dp = intel_attached_dp(connector);
>  
>  		if (!drm_dp_sink_can_do_video_without_timing_msa(intel_dp->dpcd))
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel