[PATCH] drm/i915/dp: Fix potential infinite loop in 128b/132b SST

[Jani Nikula <jani.nikula@intel.com>]

Passing 0 as the step only works when there are other reasons to break
out of the BPP loop in intel_dp_mtp_tu_compute_config(). Otherwise, an
infinite loop might occur. Fix it by explicitly checking for 0 step.

Fixes: ef0a0757bbea ("drm/i915/dp: compute config for 128b/132b SST w/o DSC")
Reported-by: Imre Deak <imre.deak@intel.com>
Closes: https://lore.kernel.org/r/Z6I0knh2Kt5T0JrT@ideak-desk.fi.intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

---

Note: This needs a backport with (!step) for -rc1.
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 95abc6ea85eb..1587be5cd0a7 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -353,6 +353,10 @@ int intel_dp_mtp_tu_compute_config(struct intel_dp *intel_dp,
 
 			break;
 		}
+
+		/* Allow using zero step to indicate one try */
+		if (!bpp_step_x16)
+			break;
 	}
 
 	if (slots < 0) {
-- 
2.39.5