On Mon, 24 Feb 2025, Imre Deak <imre.deak@xxxxxxxxx> wrote:
> The encoder HW/SW state verification should use a SW state which stays
> unchanged while the encoder/output is active. The intel_dp::is_mst flag
> used during state computation to choose between the DP SST/MST modes can
> change while the output is active, if the sink gets disconnected or the
> MST topology is removed for another reason. A subsequent state
> verification using intel_dp::is_mst leads then to a mismatch if the
> output is disabled/re-enabled without recomputing its state.
>
> Use the encoder's active MST link count instead, which will be always
> non-zero for an active MST output and will be zero for SST.
>
> Fixes: 35d2e4b75649 ("drm/i915/ddi: start distinguishing 128b/132b SST and MST at state readout")
> Fixes: 40d489fac0e8 ("drm/i915/ddi: handle 128b/132b SST in intel_ddi_read_func_ctl()")
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
Do we have a bug for this?
> ---
> drivers/gpu/drm/i915/display/intel_ddi.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index 7937f4de66cb4..8c8b53414da67 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -890,7 +890,7 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
> encoder->base.base.id, encoder->base.name);
>
> if (!mst_pipe_mask && dp128b132b_pipe_mask) {
> - struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> + struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
>
> /*
> * If we don't have 8b/10b MST, but have more than one
> @@ -902,7 +902,8 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
> * we don't expect MST to have been enabled at that point, and
> * can assume it's SST.
> */
> - if (hweight8(dp128b132b_pipe_mask) > 1 || intel_dp->is_mst)
> + if (hweight8(dp128b132b_pipe_mask) > 1 ||
> + intel_dp_mst_encoder_active_links(dig_port))
I think the reasoning here is valid, but I think we should probably do
something about the intel_dp_mst_encoder_active_links() naming as
follow-up. This is confusing. What is an "mst encoder"? The above
expects the primary digital port, i.e. it assumes enc_to_dig_port()
already did the right thing. It's all really subtle. Also wrt which
encoders the intel_ddi_get_encoder_pipes() gets called on.
Maybe we need s/intel_dp_mst_encoder/intel_dp_mst_primary/ for this and
some other functions? They're not about the "fake" mst stream encoders.
Anyway,
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> mst_pipe_mask = dp128b132b_pipe_mask;
> }
>
> @@ -4131,13 +4132,13 @@ static void intel_ddi_read_func_ctl(struct intel_encoder *encoder,
> } else if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST) {
> intel_ddi_read_func_ctl_dp_mst(encoder, pipe_config, ddi_func_ctl);
> } else if (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display)) {
> - struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> + struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
>
> /*
> * If this is true, we know we're being called from mst stream
> * encoder's ->get_config().
> */
> - if (intel_dp->is_mst)
> + if (intel_dp_mst_encoder_active_links(dig_port))
> intel_ddi_read_func_ctl_dp_mst(encoder, pipe_config, ddi_func_ctl);
> else
> intel_ddi_read_func_ctl_dp_sst(encoder, pipe_config, ddi_func_ctl);
--
Jani Nikula, Intel
