From 29b27657dbae8d4c4bdc6bfbf6dd8c69f648e075 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Wed, 2 Oct 2019 19:25:05 +0300 Subject: [PATCH] drm/i915/mst: Document the userspace fail with possible_crtcs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Link: https://patchwork.freedesktop.org/patch/msgid/20191002162505.30716-6-ville.syrjala@linux.intel.com Reviewed-by: Juha-Pekka Heikkila --- drivers/gpu/drm/i915/display/intel_dp_mst.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c index 7370c9dfa8a1..715b7109c388 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c @@ -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;