On Thu, Oct 04, 2018 at 08:29:53PM -0400, Lyude Paul wrote:

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 lyude@redhat.com Cc: stable@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) {

Wondered why you don't need this for nouveau/amdgpu, but a bit of grepping later says they don't even bother to check that in their atomic_check functions. So if a multi-stream cable runs out of vcpi slots, they just toss up their hands, atomic be damned :-(

With the s/mst_port_gone/READ_ONCE(!conn->registered)/ bikeshed:

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

I wondered a bit whether ths fuction shouldn't just return 0 if the connector is gone, but we'd need to audit/fix other drivers first. -Daniel

• 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