drm/i915/dp: Validate the compliance test link parameters

Validate the compliance test link parameters when the compliance
test dpcd registers are read. Also validate them in compute_config
before using them since the max values might have been reduced
due to link training fallback.

If either the link rate or lane count is invalid, we still bail
from using the test parameters since the combination would not work
and instead use the fallback values.

v2:
* Added commit message to explain why we still bail when either of
of the params is invalid (Ville Syrjala)
* Add reason for validating in the comment (Jani Nikula)
* Also check if index >= 0 after validating (Jani Nikula)
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1496954463-18038-2-git-send-email-manasi.d.navare@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -1690,6 +1690,11 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 	if (intel_dp->compliance.test_type == DP_TEST_LINK_TRAINING) {
 		int index;
 
+		/* Validate the compliance test data since max values
+		 * might have changed due to link train fallback.
+		 */
+		if (intel_dp_link_params_valid(intel_dp, intel_dp->compliance.test_link_rate,
+					       intel_dp->compliance.test_lane_count)) {
 			index = intel_dp_rate_index(intel_dp->common_rates,
 						    intel_dp->num_common_rates,
 						    intel_dp->compliance.test_link_rate);
@@ -1697,6 +1702,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 				min_clock = max_clock = index;
 			min_lane_count = max_lane_count = intel_dp->compliance.test_lane_count;
 		}
+	}
 	DRM_DEBUG_KMS("DP link computation with max lane count %i "
 		      "max bw %d pixel clock %iKHz\n",
 		      max_lane_count, intel_dp->common_rates[max_clock],
@@ -3976,8 +3982,7 @@ intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *sink_irq_vector)
 static uint8_t intel_dp_autotest_link_training(struct intel_dp *intel_dp)
 {
 	int status = 0;
-	int min_lane_count = 1;
-	int link_rate_index, test_link_rate;
+	int test_link_rate;
 	uint8_t test_lane_count, test_link_bw;
 	/* (DP CTS 1.2)
 	 * 4.3.1.11
@@ -3991,10 +3996,6 @@ static uint8_t intel_dp_autotest_link_training(struct intel_dp *intel_dp)
 		return DP_TEST_NAK;
 	}
 	test_lane_count &= DP_MAX_LANE_COUNT_MASK;
-	/* Validate the requested lane count */
-	if (test_lane_count < min_lane_count ||
-	    test_lane_count > intel_dp->max_link_lane_count)
-		return DP_TEST_NAK;
 
 	status = drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_LINK_RATE,
 				   &test_link_bw);
@@ -4002,12 +4003,11 @@ static uint8_t intel_dp_autotest_link_training(struct intel_dp *intel_dp)
 		DRM_DEBUG_KMS("Link Rate read failed\n");
 		return DP_TEST_NAK;
 	}
-	/* Validate the requested link rate */
 	test_link_rate = drm_dp_bw_code_to_link_rate(test_link_bw);
-	link_rate_index = intel_dp_rate_index(intel_dp->common_rates,
-					      intel_dp->num_common_rates,
-					      test_link_rate);
-	if (link_rate_index < 0)
+
+	/* Validate the requested link rate and lane count */
+	if (!intel_dp_link_params_valid(intel_dp, test_link_rate,
+					test_lane_count))
 		return DP_TEST_NAK;
 
 	intel_dp->compliance.test_lane_count = test_lane_count;