drm/i915/hotplug: Use phy to get the hpd_pin instead of the port (v5)

On some platforms such as Elkhart Lake, although we may use DDI D
to drive a connector, we have to use PHY A (Combo Phy PORT A) to
detect the hotplug interrupts as per the spec because there is no
one-to-one mapping between DDIs and PHYs. Therefore, use the
function intel_port_to_phy() which contains the logic for such
mapping(s) to find the correct hpd_pin.

This change should not affect other platforms as there is always
a one-to-one mapping between DDIs and PHYs.

v2:
- Convert the case statements to use PHYs instead of PORTs (Jani)

v3:
- Refactor the function to reduce the number of return statements by
  lumping all the case statements together except PHY_F which needs
  special handling (Jose)

v4:
- Add a comment describing how the HPD pin value associated with any
  port can be retrieved using port or phy enum value. (Jani)

v5:
- Use case ranges instead of individual labels and also normalize the
  return statement by adding -PHY_A to the expression (Ville)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200304234240.12062-1-vivek.kasireddy@intel.com

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

@@ -87,29 +87,16 @@
 enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
 				   enum port port)
 {
-	switch (port) {
-	case PORT_A:
-		return HPD_PORT_A;
-	case PORT_B:
-		return HPD_PORT_B;
-	case PORT_C:
-		return HPD_PORT_C;
-	case PORT_D:
-		return HPD_PORT_D;
-	case PORT_E:
-		return HPD_PORT_E;
-	case PORT_F:
-		if (IS_CNL_WITH_PORT_F(dev_priv))
-			return HPD_PORT_E;
-		return HPD_PORT_F;
-	case PORT_G:
-		return HPD_PORT_G;
-	case PORT_H:
-		return HPD_PORT_H;
-	case PORT_I:
-		return HPD_PORT_I;
+	enum phy phy = intel_port_to_phy(dev_priv, port);
+
+	switch (phy) {
+	case PHY_F:
+		return IS_CNL_WITH_PORT_F(dev_priv) ? HPD_PORT_E : HPD_PORT_F;
+	case PHY_A ... PHY_E:
+	case PHY_G ... PHY_I:
+		return HPD_PORT_A + phy - PHY_A;
 	default:
-		MISSING_CASE(port);
+		MISSING_CASE(phy);
 		return HPD_NONE;
 	}
 }

drivers/gpu/drm/i915/i915_drv.h

@@ -114,6 +114,13 @@
 
 struct drm_i915_gem_object;
 
+/*
+ * The code assumes that the hpd_pins below have consecutive values and
+ * starting with HPD_PORT_A, the HPD pin associated with any port can be
+ * retrieved by adding the corresponding port (or phy) enum value to
+ * HPD_PORT_A in most cases. For example:
+ * HPD_PORT_C = HPD_PORT_A + PHY_C - PHY_A
+ */
 enum hpd_pin {
 	HPD_NONE = 0,
 	HPD_TV = HPD_NONE,     /* TV is known to be unreliable */