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drm/i915/mst: Document the userspace fail with possible_crtcs

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To avoid accidentally breaking things in the future add a
comment explaining why we misconfigure the pipe_mask.

Also toss in a TODO for investigating a single encoder
approach as opposed to the encoder-per-pipe approach.

v2: Drop a bogus TODO comment

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191002162505.30716-6-ville.syrjala@linux.intel.com
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
This commit is contained in:
Ville Syrjälä 2019-10-02 19:25:05 +03:00
parent 34053ee189
commit 29b27657db
1 changed files with 8 additions and 0 deletions
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8
drivers/gpu/drm/i915/display/intel_dp_mst.c
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@ -615,6 +615,14 @@ intel_dp_create_fake_mst_encoder(struct intel_digital_port *intel_dig_port, enum
intel_encoder->power_domain = intel_dig_port->base.power_domain;
intel_encoder->port = intel_dig_port->base.port;
intel_encoder->cloneable = 0;
/*
* This is wrong, but broken userspace uses the intersection
* of possible_crtcs of all the encoders of a given connector
* to figure out which crtcs can drive said connector. What
* should be used instead is the union of possible_crtcs.
* To keep such userspace functioning we must misconfigure
* this to make sure the intersection is not empty :(
*/
intel_encoder->pipe_mask = ~0;
intel_encoder->compute_config = intel_dp_mst_compute_config;