[PATCH] drm/i915/display: Check some INVALID_TRANSCODER cases

[Jonathan Cavitt <jonathan.cavitt@intel.com>]

There are some cases in intel_ddi.c, such as in intel_ddi_is_audio_enabled
and intel_ddi_compute_config_late, where we attempt to perform a BIT
shift using a passed transcoder enum value.  This value may be -1,
INVALID_TRANSCODER, which can result in undefined behavior if this
occurs.

In the former case, we can simply return false if this is the transcoder
passed (as audio is not enabled on an invalid transcoder).

In the latter case, the likely expected behavior is to set the
crtc_state->sync_mode_slaves_mask to zero, so just do that directly and
avoid a risky bit shift.

The likelihood of either case occurring during normal execution is
unknown and possibly very low.  Regardless, this covers a static analyis
issue.

Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
---
 drivers/gpu/drm/i915/display/intel_ddi.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
index 178074316a2c..7abeb60779e5 100644
--- a/drivers/gpu/drm/i915/display/intel_ddi.c
+++ b/drivers/gpu/drm/i915/display/intel_ddi.c
@@ -3875,7 +3875,8 @@ static void intel_ddi_set_idle_link_train(struct intel_dp *intel_dp,
 static bool intel_ddi_is_audio_enabled(struct intel_display *display,
 				       enum transcoder cpu_transcoder)
 {
-	if (cpu_transcoder == TRANSCODER_EDP)
+	if (cpu_transcoder == TRANSCODER_EDP ||
+	    cpu_transcoder == INVALID_TRANSCODER)
 		return false;
 
 	if (!intel_display_power_is_enabled(display, POWER_DOMAIN_AUDIO_MMIO))
@@ -4637,8 +4638,13 @@ static int intel_ddi_compute_config_late(struct intel_encoder *encoder,
 
 	if (crtc_state->master_transcoder == crtc_state->cpu_transcoder) {
 		crtc_state->master_transcoder = INVALID_TRANSCODER;
-		crtc_state->sync_mode_slaves_mask =
-			port_sync_transcoders & ~BIT(crtc_state->cpu_transcoder);
+		if (crtc_state->cpu_transcoder == INVALID_TRANSCODER ||
+		    !port_sync_transcoders)
+			crtc_state->sync_mode_slaves_mask = 0;
+		else
+
+			crtc_state->sync_mode_slaves_mask =
+				port_sync_transcoders & ~BIT(crtc_state->cpu_transcoder);
 	}
 
 	return 0;
-- 
2.43.0