drm: provide a helper for the encoder possible_crtcs mask

The encoder possible_crtcs mask identifies which CRTCs can be bound to
a particular encoder.  Each bit from bit 0 defines an index in the list
of CRTCs held in the DRM mode_config crtc_list.  Rather than having
drivers trying to track the position of their CRTCs in the list, expose
the code which already exists for calculating the appropriate mask bit
for a CRTC.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
[treding@nvidia.com: add drm_crtc_index(), move to core]
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/drm_crtc.c

@@ -674,6 +674,29 @@ void drm_crtc_cleanup(struct drm_crtc *crtc)
 }
 EXPORT_SYMBOL(drm_crtc_cleanup);
 
+/**
+ * drm_crtc_index - find the index of a registered CRTC
+ * @crtc: CRTC to find index for
+ *
+ * Given a registered CRTC, return the index of that CRTC within a DRM
+ * device's list of CRTCs.
+ */
+unsigned int drm_crtc_index(struct drm_crtc *crtc)
+{
+	unsigned int index = 0;
+	struct drm_crtc *tmp;
+
+	list_for_each_entry(tmp, &crtc->dev->mode_config.crtc_list, head) {
+		if (tmp == crtc)
+			return index;
+
+		index++;
+	}
+
+	BUG();
+}
+EXPORT_SYMBOL(drm_crtc_index);
+
 /**
  * drm_mode_probed_add - add a mode to a connector's probed mode list
  * @connector: connector the new mode

drivers/gpu/drm/drm_crtc_helper.c

@@ -334,23 +334,7 @@ EXPORT_SYMBOL(drm_helper_disable_unused_functions);
 static bool drm_encoder_crtc_ok(struct drm_encoder *encoder,
 				struct drm_crtc *crtc)
 {
-	struct drm_device *dev;
-	struct drm_crtc *tmp;
-	int crtc_mask = 1;
-
-	WARN(!crtc, "checking null crtc?\n");
-
-	dev = crtc->dev;
-
-	list_for_each_entry(tmp, &dev->mode_config.crtc_list, head) {
-		if (tmp == crtc)
-			break;
-		crtc_mask <<= 1;
-	}
-
-	if (encoder->possible_crtcs & crtc_mask)
-		return true;
-	return false;
+	return !!(encoder->possible_crtcs & drm_crtc_mask(crtc));
 }
 
 /*

include/drm/drm_crtc.h

@@ -929,6 +929,19 @@ extern int drm_crtc_init(struct drm_device *dev,
 			 struct drm_crtc *crtc,
 			 const struct drm_crtc_funcs *funcs);
 extern void drm_crtc_cleanup(struct drm_crtc *crtc);
+extern unsigned int drm_crtc_index(struct drm_crtc *crtc);
+
+/**
+ * drm_crtc_mask - find the mask of a registered CRTC
+ * @crtc: CRTC to find mask for
+ *
+ * Given a registered CRTC, return the mask bit of that CRTC for an
+ * encoder's possible_crtcs field.
+ */
+static inline uint32_t drm_crtc_mask(struct drm_crtc *crtc)
+{
+	return 1 << drm_crtc_index(crtc);
+}
 
 extern void drm_connector_ida_init(void);
 extern void drm_connector_ida_destroy(void);