[PATCH 13/14] drm/i915/dp_mst: Ensure link parameters are up-to-date for a disabled link

[Kandpal, Suraj]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Imre
> Deak
> Sent: Monday, July 22, 2024 10:25 PM
> To: intel-gfx at lists.freedesktop.org
> Subject: [PATCH 13/14] drm/i915/dp_mst: Ensure link parameters are up-to-
> date for a disabled link
> 
> As explained in the previous patch, the MST link BW reported by branch
> devices during topology probing/path resources enumeration depends on
> the link parameters programmed to DPCD to be up-to-date. After a sink is

I think you maybe missed a couple of words here maybe fix that
Rest LGTM
Reviewed-by: Suraj Kandpal <suraj.kandpal at intel.com>

> plugged this is not ensured, as those DPCD values start out zeroed. The
> target link parameters (for a subsequent modeset) are the maximum that is
> supported, so make sure these maximum values are programmed before
> the topology probing.
> 
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c     |  3 ++
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 31 +++++++++++++++++++++
> drivers/gpu/drm/i915/display/intel_dp_mst.h |  1 +
>  3 files changed, 35 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index 0771e4c6357ba..41f5d82ca75d8 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4262,6 +4262,9 @@ intel_dp_mst_configure(struct intel_dp *intel_dp)
> 
>  	intel_dp->is_mst = intel_dp->mst_detect != DRM_DP_SST;
> 
> +	if (intel_dp->is_mst)
> +		intel_dp_mst_prepare_probe(intel_dp);
> +
>  	drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, intel_dp-
> >is_mst);
> 
>  	/* Avoid stale info on the next detect cycle. */ diff --git
> a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 19c8b6878b030..faee7af0a8a48 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -43,6 +43,7 @@
>  #include "intel_dp_hdcp.h"
>  #include "intel_dp_mst.h"
>  #include "intel_dp_tunnel.h"
> +#include "intel_dp_link_training.h"
>  #include "intel_dpio_phy.h"
>  #include "intel_hdcp.h"
>  #include "intel_hotplug.h"
> @@ -2031,3 +2032,33 @@ bool intel_dp_mst_crtc_needs_modeset(struct
> intel_atomic_state *state,
> 
>  	return false;
>  }
> +
> +/**
> + * intel_dp_mst_prepare_probe - Prepare an MST link for topology
> +probing
> + * @intel_dp: DP port object
> + *
> + * Prepare an MST link for topology probing, programming the target
> + * link parameters to DPCD. This step is a requirement of the
> +enumaration
> + * of path resources during probing.
> + */
> +void intel_dp_mst_prepare_probe(struct intel_dp *intel_dp) {
> +	int link_rate = intel_dp_max_link_rate(intel_dp);
> +	int lane_count = intel_dp_max_lane_count(intel_dp);
> +	u8 rate_select;
> +	u8 link_bw;
> +
> +	if (intel_dp->link_trained)
> +		return;
> +
> +	if (intel_mst_probed_link_params_valid(intel_dp, link_rate,
> lane_count))
> +		return;
> +
> +	intel_dp_compute_rate(intel_dp, link_rate, &link_bw, &rate_select);
> +
> +	intel_dp_link_training_set_mode(intel_dp, link_rate, false);
> +	intel_dp_link_training_set_bw(intel_dp, link_bw, rate_select,
> lane_count,
> +				      drm_dp_enhanced_frame_cap(intel_dp-
> >dpcd));
> +
> +	intel_mst_set_probed_link_params(intel_dp, link_rate, lane_count);
> }
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.h
> b/drivers/gpu/drm/i915/display/intel_dp_mst.h
> index 8ca1d599091c6..fba76454fa67f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.h
> @@ -27,5 +27,6 @@ int intel_dp_mst_atomic_check_link(struct
> intel_atomic_state *state,
>  				   struct intel_link_bw_limits *limits);  bool
> intel_dp_mst_crtc_needs_modeset(struct intel_atomic_state *state,
>  				     struct intel_crtc *crtc);
> +void intel_dp_mst_prepare_probe(struct intel_dp *intel_dp);
> 
>  #endif /* __INTEL_DP_MST_H__ */
> --
> 2.44.2