Re: [PATCH] drm/i915/dp: Fix DSC state computation

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 3/2/2026 3:58 PM, Imre Deak wrote:
> When computing the encoder/CRTC state multiple times, such as during
> iteration over the possible pipe joiner configurations, it must be
> ensured that all state is explicitly initialized each time. At the
> moment, this is not guaranteed for the DSC/FEC state within the
> encoder/CRTC state. In one iteration trying a pipe joiner configuration,
> the DSC state may get initialized without computing the full
> CRTC/encoder state due to the given joiner configuration being
> impossible. When the same CRTC/encoder state is recomputed in a
> subsequent iteration, the previously set non-zero - now stale - DSC/FEC
> state may still be present, which is unexpected if a non-DSC
> configuration is being computed.
>
> This can lead to a DSC state mismatch error if multiple joiner
> configurations are evaluated and the working configuration ultimately
> turns out to be a non-DSC one.
>
> Follow the existing pattern and compute the full (DSC/FEC) state on all
> code paths (including now the non-DSC path as well) to fix the issue.
>
> Fixes: 1f1e3e5c65f6 ("drm/i915/dp: Rework pipe joiner logic in compute_config")
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7512
> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>

LGTM.

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>


> ---
>   drivers/gpu/drm/i915/display/intel_dp.c     | 13 +++++++++++++
>   drivers/gpu/drm/i915/display/intel_dp.h     |  1 +
>   drivers/gpu/drm/i915/display/intel_dp_mst.c |  2 ++
>   3 files changed, 16 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 6c25c7595c48..2d9ce21e5bbe 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2457,6 +2457,17 @@ bool intel_dp_needs_8b10b_fec(const struct intel_crtc_state *crtc_state,
>   	return dsc_enabled_on_crtc || intel_dsc_enabled_on_link(crtc_state);
>   }
>   
> +void intel_dp_dsc_reset_config(struct intel_crtc_state *crtc_state)
> +{
> +	crtc_state->fec_enable = false;
> +
> +	crtc_state->dsc.compression_enable = false;
> +	crtc_state->dsc.compressed_bpp_x16 = 0;
> +
> +	memset(&crtc_state->dsc.slice_config, 0, sizeof(crtc_state->dsc.slice_config));
> +	memset(&crtc_state->dsc.config, 0, sizeof(crtc_state->dsc.config));
> +}
> +
>   int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
>   				struct intel_crtc_state *pipe_config,
>   				struct drm_connector_state *conn_state,
> @@ -2888,6 +2899,8 @@ intel_dp_compute_link_for_joined_pipes(struct intel_encoder *encoder,
>   	bool dsc_needed, joiner_needs_dsc;
>   	int ret = 0;
>   
> +	intel_dp_dsc_reset_config(pipe_config);
> +
>   	joiner_needs_dsc = intel_dp_joiner_needs_dsc(display, num_joined_pipes);
>   
>   	dsc_needed = joiner_needs_dsc || intel_dp->force_dsc_en ||
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index 57fac7fb837f..fbe43ca3d99f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -75,6 +75,7 @@ int intel_dp_compute_config(struct intel_encoder *encoder,
>   			    struct drm_connector_state *conn_state);
>   bool intel_dp_needs_8b10b_fec(const struct intel_crtc_state *crtc_state,
>   			      bool dsc_enabled_on_crtc);
> +void intel_dp_dsc_reset_config(struct intel_crtc_state *crtc_state);
>   int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
>   				struct intel_crtc_state *pipe_config,
>   				struct drm_connector_state *conn_state,
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index e73ae4956f9b..90349819dcfb 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -610,6 +610,8 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>   	bool dsc_needed, joiner_needs_dsc;
>   	int ret = 0;
>   
> +	intel_dp_dsc_reset_config(pipe_config);
> +
>   	joiner_needs_dsc = intel_dp_joiner_needs_dsc(display, num_joined_pipes);
>   
>   	dsc_needed = joiner_needs_dsc || intel_dp->force_dsc_en ||