[PATCH] drm/i915/dp_mst: Fix MST state after a sink reset

[Jani Nikula]

On Wed, 24 Jul 2024, Imre Deak <imre.deak at intel.com> wrote:
> In some cases the sink can reset itself after it was configured into MST
> mode, without the driver noticing the disconnected state. For instance
> the reset may happen in the middle of a modeset, or the (long) HPD pulse
> generated may be not long enough for the encoder detect handler to
> observe the HPD's deasserted state. In this case the sink's DPCD
> register programmed to enable MST will be reset, while the driver still
> assumes MST is still enabled. Detect this condition, which will tear
> down and recreate/re-enable the MST topology.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11195
> 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 | 30 +++++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_dp_mst.h |  1 +
>  3 files changed, 34 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 1e43e32e05199..c621f6daf8235 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5878,6 +5878,9 @@ intel_dp_detect(struct drm_connector *connector,
>  	else
>  		status = connector_status_disconnected;
>  
> +	if (!intel_dp_mst_verify_dpcd_state(intel_dp))
> +		status = connector_status_disconnected;
> +

So I still don't understand. We've got a detect which we've determined
is connected. But then we disconnect because the sink state has changed.

How do we get another connect?

BR,
Jani.


>  	if (status == connector_status_disconnected) {
>  		memset(&intel_dp->compliance, 0, sizeof(intel_dp->compliance));
>  		memset(intel_connector->dp.dsc_dpcd, 0, sizeof(intel_connector->dp.dsc_dpcd));
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 27ce5c3f5951e..89b147e37b400 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -1998,3 +1998,33 @@ bool intel_dp_mst_crtc_needs_modeset(struct intel_atomic_state *state,
>  
>  	return false;
>  }
> +
> +/**
> + * intel_dp_mst_verify_dpcd_state - verify the MST SW enabled state wrt. the DPCD
> + * @intel_dp: DP port object
> + *
> + * Verify if @intel_dp's MST enabled SW state matches the corresponding DPCD
> + * state. A long HPD pulse -not long enough to be detected as a disconnected
> + * state - could've reset the DPCD state, which requires tearing
> + * down/recreating the MST topology.
> + *
> + * Returns %true if the SW MST enabled and DPCD states match, %false
> + * otherwise.
> + */
> +bool intel_dp_mst_verify_dpcd_state(struct intel_dp *intel_dp)
> +{
> +	int ret;
> +	u8 val;
> +
> +	if (!intel_dp->is_mst)
> +		return true;
> +
> +	ret = drm_dp_dpcd_readb(intel_dp->mst_mgr.aux, DP_MSTM_CTRL, &val);
> +	if (ret < 0)
> +		return false;
> +
> +	if (val != (DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC))
> +		return false;
> +
> +	return true;
> +}
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.h b/drivers/gpu/drm/i915/display/intel_dp_mst.h
> index 8ca1d599091c6..9e4c7679f1c3a 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);
> +bool intel_dp_mst_verify_dpcd_state(struct intel_dp *intel_dp);
>  
>  #endif /* __INTEL_DP_MST_H__ */

-- 
Jani Nikula, Intel