drm: Add drm_connector_for_each_possible_encoder()

Add a convenience macro for iterating connector->encoder_ids[].
Isolates the users from the implementation details.

Note that we don't seem to pass the file_priv down to drm_encoder_find()
because encoders apparently don't get leased. No idea why
drm_encoder_finc() even takes the file_priv actually.

Also use ARRAY_SIZE() when populating the array to avoid spreading
knowledge about the array size all over.

v2: Hide the drm_encoder_find() in the macro, and
    rename the macro appropriately (Daniel)
v3: Fix kernel docs (Daniel)

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180628131315.14156-4-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_connector.c

@@ -321,7 +321,7 @@ int drm_mode_connector_attach_encoder(struct drm_connector *connector,
 	if (WARN_ON(connector->encoder))
 		return -EINVAL;
 
-	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
+	for (i = 0; i < ARRAY_SIZE(connector->encoder_ids); i++) {
 		if (connector->encoder_ids[i] == 0) {
 			connector->encoder_ids[i] = encoder->base.id;
 			return 0;
@@ -1706,22 +1706,19 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 	if (!connector)
 		return -ENOENT;
 
-	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++)
-		if (connector->encoder_ids[i] != 0)
-			encoders_count++;
+	drm_connector_for_each_possible_encoder(connector, encoder, i)
+		encoders_count++;
 
 	if ((out_resp->count_encoders >= encoders_count) && encoders_count) {
 		copied = 0;
 		encoder_ptr = (uint32_t __user *)(unsigned long)(out_resp->encoders_ptr);
-		for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
-			if (connector->encoder_ids[i] != 0) {
-				if (put_user(connector->encoder_ids[i],
-					     encoder_ptr + copied)) {
-					ret = -EFAULT;
-					goto out;
-				}
-				copied++;
+
+		drm_connector_for_each_possible_encoder(connector, encoder, i) {
+			if (put_user(encoder->base.id, encoder_ptr + copied)) {
+				ret = -EFAULT;
+				goto out;
 			}
+			copied++;
 		}
 	}
 	out_resp->count_encoders = encoders_count;

drivers/gpu/drm/drm_fb_helper.c

@@ -2326,17 +2326,10 @@ static bool drm_target_preferred(struct drm_fb_helper *fb_helper,
 static bool connector_has_possible_crtc(struct drm_connector *connector,
 					struct drm_crtc *crtc)
 {
+	struct drm_encoder *encoder;
 	int i;
 
-	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
-		struct drm_encoder *encoder;
-
-		if (connector->encoder_ids[i] == 0)
-			break;
-
-		encoder = drm_encoder_find(connector->dev, NULL,
-					   connector->encoder_ids[i]);
-
+	drm_connector_for_each_possible_encoder(connector, encoder, i) {
 		if (encoder->possible_crtcs & drm_crtc_mask(crtc))
 			return true;
 	}

drivers/gpu/drm/drm_probe_helper.c

@@ -88,23 +88,19 @@ drm_mode_validate_pipeline(struct drm_display_mode *mode,
 			    struct drm_connector *connector)
 {
 	struct drm_device *dev = connector->dev;
-	uint32_t *ids = connector->encoder_ids;
 	enum drm_mode_status ret = MODE_OK;
-	unsigned int i;
+	struct drm_encoder *encoder;
+	int i;
 
 	/* Step 1: Validate against connector */
 	ret = drm_connector_mode_valid(connector, mode);
 	if (ret != MODE_OK)
 		return ret;
 
 	/* Step 2: Validate against encoders and crtcs */
-	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
-		struct drm_encoder *encoder = drm_encoder_find(dev, NULL, ids[i]);
+	drm_connector_for_each_possible_encoder(connector, encoder, i) {
 		struct drm_crtc *crtc;
 
-		if (!encoder)
-			continue;
-
 		ret = drm_encoder_mode_valid(encoder, mode);
 		if (ret != MODE_OK) {
 			/* No point in continuing for crtc check as this encoder

include/drm/drm_connector.h

@@ -1199,4 +1199,17 @@ void drm_connector_list_iter_end(struct drm_connector_list_iter *iter);
 #define drm_for_each_connector_iter(connector, iter) \
 	while ((connector = drm_connector_list_iter_next(iter)))
 
+/**
+ * drm_connector_for_each_possible_encoder - iterate connector's possible encoders
+ * @connector: &struct drm_connector pointer
+ * @encoder: &struct drm_encoder pointer used as cursor
+ * @__i: int iteration cursor, for macro-internal use
+ */
+#define drm_connector_for_each_possible_encoder(connector, encoder, __i) \
+	for ((__i) = 0; (__i) < ARRAY_SIZE((connector)->encoder_ids) && \
+		     (connector)->encoder_ids[(__i)] != 0; (__i)++) \
+		for_each_if((encoder) = \
+			    drm_encoder_find((connector)->dev, NULL, \
+					     (connector)->encoder_ids[(__i)])) \
+
 #endif