drm/i915: Drop AUX backlight enable check for backlight control

There are some panel that
(1) does not support display backlight enable via AUX
(2) support display backlight adjustment via AUX
(3) support display backlight enable via eDP BL_ENABLE pin

The current driver required that (1) must be support to enable (2).
This patch drops that requirement.
Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170523223805.46372-2-puthik@chromium.org

drivers/gpu/drm/i915/intel_dp_aux_backlight.c

@@ -28,6 +28,10 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
 {
 	uint8_t reg_val = 0;
 
+	/* Early return when display use other mechanism to enable backlight. */
+	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
+		return;
+
 	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
 			      &reg_val) < 0) {
 		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
@@ -165,10 +169,8 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
 	 * the panel can support backlight control over the aux channel
 	 */
 	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
-	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
 	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
-	    !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) ||
-	      (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))) {
+	    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
 		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
 		return true;
 	}