[PATCH] drm/i915/dp: fix shifting by a negative number of bits

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

Function intel_port_to_tc() returns PORT_TC_NONE on error, which is
a negative value -1. In case PORT_TC_NONE is returned, there is an
undefined behavior when shifting by a negative number of bits in
both DP_PHY_MODE_STATUS_NOT_SAFE and P_PHY_MODE_STATUS_COMPLETED
macros.

Fix this by adding sanity checks on intel_port_to_tc return value, before
using macros DP_PHY_MODE_STATUS_NOT_SAFE and P_PHY_MODE_STATUS_COMPLETED.

Addresses-Coverity-ID: 1473324 ("Bad bit shift operation")
Addresses-Coverity-ID: 1473325 ("Bad bit shift operation")
Fixes: 39d1e234e1e1 ("drm/i915/icl: implement the tc/legacy HPD {dis,}connect flows")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 436c22d..e34b7b1 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4811,6 +4811,11 @@ static bool icl_tc_phy_connect(struct drm_i915_private *dev_priv,
 	    dig_port->tc_type != TC_PORT_TYPEC)
 		return true;
 
+	if (tc_port < 0) {
+		DRM_DEBUG_KMS("Bad TC port %d\n", tc_port);
+		return false;
+	}
+
 	val = I915_READ(PORT_TX_DFLEXDPPMS);
 	if (!(val & DP_PHY_MODE_STATUS_COMPLETED(tc_port))) {
 		DRM_DEBUG_KMS("DP PHY for TC port %d not ready\n", tc_port);
@@ -4857,6 +4862,10 @@ static void icl_tc_phy_disconnect(struct drm_i915_private *dev_priv,
 	    dig_port->tc_type != TC_PORT_TYPEC)
 		return;
 
+	if (tc_port < 0) {
+		DRM_DEBUG_KMS("Bad TC port %d\n", tc_port);
+		return;
+	}
 	/*
 	 * This function may be called many times in a row without an HPD event
 	 * in between, so try to avoid the write when we can.
-- 
2.7.4