Since we need to be able to allow DPMS on->off prop changes after an MST
port has disappeared from the system, we need to be able to make sure we
can compute a config for the resulting atomic commit. Currently this is
impossible when the port has disappeared, since the VCPI slot searching
we try to do in intel_dp_mst_compute_config() will fail with -EINVAL.

Since the only commits we want to allow on no-longer-present MST ports
are ones that shut off display hardware, we already know that no VCPI
allocations are needed. So, hardcode the VCPI slot count to 0 when
intel_dp_mst_compute_config() is called on an MST port that's gone.

Signed-off-by: Lyude Paul <ly...@redhat.com>
Cc: sta...@vger.kernel.org
---
 drivers/gpu/drm/i915/intel_dp_mst.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c 
b/drivers/gpu/drm/i915/intel_dp_mst.c
index fcb9b87b9339..a366f32b048a 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -42,7 +42,7 @@ static bool intel_dp_mst_compute_config(struct intel_encoder 
*encoder,
                to_intel_connector(conn_state->connector);
        struct drm_atomic_state *state = pipe_config->base.state;
        int bpp;
-       int lane_count, slots;
+       int lane_count, slots = 0;
        const struct drm_display_mode *adjusted_mode = 
&pipe_config->base.adjusted_mode;
        int mst_pbn;
        bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc,
@@ -76,11 +76,16 @@ static bool intel_dp_mst_compute_config(struct 
intel_encoder *encoder,
        mst_pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock, bpp);
        pipe_config->pbn = mst_pbn;
 
-       slots = drm_dp_atomic_find_vcpi_slots(state, &intel_dp->mst_mgr,
-                                             connector->port, mst_pbn);
-       if (slots < 0) {
-               DRM_DEBUG_KMS("failed finding vcpi slots:%d\n", slots);
-               return false;
+       if (!connector->mst_port_gone) {
+               slots = drm_dp_atomic_find_vcpi_slots(state,
+                                                     &intel_dp->mst_mgr,
+                                                     connector->port,
+                                                     mst_pbn);
+               if (slots < 0) {
+                       DRM_DEBUG_KMS("failed finding vcpi slots:%d\n",
+                                     slots);
+                       return false;
+               }
        }
 
        intel_link_compute_m_n(bpp, lane_count,
-- 
2.17.1

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