drm/i915: Pick the backlight controller based on VBT on ICP+

Use the second backlight controller on ICP+ if the VBT asks
us to do so.

On pre-MTP we also check the chicken bit to make sure the
pins have been correctly muxed by the firmware.

Cc: stable@vger.kernel.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8016
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230207064337.18697-4-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit b337715)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Author: vsyrjala

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

@@ -1431,6 +1431,30 @@ bxt_setup_backlight(struct intel_connector *connector, enum pipe unused)
 	return 0;
 }
 
+static int cnp_num_backlight_controllers(struct drm_i915_private *i915)
+{
+	if (INTEL_PCH_TYPE(i915) >= PCH_DG1)
+		return 1;
+
+	if (INTEL_PCH_TYPE(i915) >= PCH_ICP)
+		return 2;
+
+	return 1;
+}
+
+static bool cnp_backlight_controller_is_valid(struct drm_i915_private *i915, int controller)
+{
+	if (controller < 0 || controller >= cnp_num_backlight_controllers(i915))
+		return false;
+
+	if (controller == 1 &&
+	    INTEL_PCH_TYPE(i915) >= PCH_ICP &&
+	    INTEL_PCH_TYPE(i915) < PCH_MTP)
+		return intel_de_read(i915, SOUTH_CHICKEN1) & ICP_SECOND_PPS_IO_SELECT;
+
+	return true;
+}
+
 static int
 cnp_setup_backlight(struct intel_connector *connector, enum pipe unused)
 {
@@ -1440,10 +1464,14 @@ cnp_setup_backlight(struct intel_connector *connector, enum pipe unused)
 
 	/*
 	 * CNP has the BXT implementation of backlight, but with only one
-	 * controller. TODO: ICP has multiple controllers but we only use
-	 * controller 0 for now.
+	 * controller. ICP+ can have two controllers, depending on pin muxing.
 	 */
-	panel->backlight.controller = 0;
+	panel->backlight.controller = connector->panel.vbt.backlight.controller;
+	if (!cnp_backlight_controller_is_valid(i915, panel->backlight.controller)) {
+		drm_dbg_kms(&i915->drm, "Invalid backlight controller %d, assuming 0\n",
+			    panel->backlight.controller);
+		panel->backlight.controller = 0;
+	}
 
 	pwm_ctl = intel_de_read(i915,
 				BXT_BLC_PWM_CTL(panel->backlight.controller));