[PATCH 2/4] drm/i915: Fix intel_dp_mst_compute_link_config

[Stanislav Lisovskiy]

We currently always exit that bpp loop because
drm_dp_atomic_find_vcpi_slots doesn't care if we actually
can fit those or not.
I think that wasn't the initial intention here, especially when
we keep trying with lower bpps, we are supposed to keep trying
until we actually find some _working_ configuration, which isn't the
case here.
So added that drm_dp_mst_check here, so that we can make sure
that try all the bpps before we fail.

Reviewed-by: Vinod Govindapillai <vinod.govindapillai at intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 7713c19042f3..24d6a287a6e3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -60,6 +60,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
 		&crtc_state->hw.adjusted_mode;
 	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CONSTANT_N);
 	int bpp, slots = -EINVAL;
+	int ret = 0;
 
 	mst_state = drm_atomic_get_mst_topology_state(state, &intel_dp->mst_mgr);
 	if (IS_ERR(mst_state))
@@ -85,10 +86,21 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
 						      connector->port, crtc_state->pbn);
 		if (slots == -EDEADLK)
 			return slots;
-		if (slots >= 0)
-			break;
+		if (slots >= 0) {
+			ret = drm_dp_mst_atomic_check(state);
+			/*
+			 * If we got slots >= 0 and we can fit those based on check
+			 * then we can exit the loop. Otherwise keep trying.
+			 */
+			if (!ret)
+				break;
+		}
 	}
 
+	/* Despite slots are non-zero, we still failed the atomic check */
+	if (ret && slots >= 0)
+		slots = ret;
+
 	if (slots < 0) {
 		drm_dbg_kms(&i915->drm, "failed finding vcpi slots:%d\n",
 			    slots);
-- 
2.37.3