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

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: ef0a075 ("drm/i915/dp: compute config for 128b/132b SST w/o DSC")
Reported-by: Imre Deak <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]
Reviewed-by: Imre Deak <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Jani Nikula <[email protected]>
(cherry picked from commit a40e718)
Signed-off-by: Rodrigo Vivi <[email protected]>

Author: jnikula

drivers/gpu/drm/i915/display/intel_dp_mst.c

@@ -341,6 +341,10 @@ int intel_dp_mtp_tu_compute_config(struct intel_dp *intel_dp,
 
 			break;
 		}
+
+		/* Allow using zero step to indicate one try */
+		if (!step)
+			break;
 	}
 
 	if (slots < 0) {