dm: core: Add a function to see if a device exists

All the uclass functions for finding a device end up creating a uclass
if it doesn't exist. Add a function which instead returns NULL in this
case.

This is useful when in the 'unbind' path, since we don't want to undo
any unbinding which has already happened.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/core/uclass.c

@@ -304,6 +304,17 @@ int uclass_find_device_by_name(enum uclass_id id, const char *name,
 	return uclass_find_device_by_namelen(id, name, strlen(name), devp);
 }
 
+struct udevice *uclass_try_first_device(enum uclass_id id)
+{
+	struct uclass *uc;
+
+	uc = uclass_find(id);
+	if (!uc || list_empty(&uc->dev_head))
+		return NULL;
+
+	return list_first_entry(&uc->dev_head, struct udevice, uclass_node);
+}
+
 int uclass_find_next_free_seq(struct uclass *uc)
 {
 	struct udevice *dev;

include/dm/uclass.h

@@ -435,6 +435,17 @@ int uclass_next_device_check(struct udevice **devp);
 int uclass_first_device_drvdata(enum uclass_id id, ulong driver_data,
 				struct udevice **devp);
 
+/**
+ * uclass_try_first_device()- See if there is a device for a uclass
+ *
+ * If the uclass exists, this returns the first device on that uclass, without
+ * probing it. If the uclass does not exist, it gives up
+ *
+ * @id: Uclass ID to check
+ * Return: Pointer to device, if found, else NULL
+ */
+struct udevice *uclass_try_first_device(enum uclass_id id);
+
 /**
  * uclass_probe_all() - Probe all devices based on an uclass ID
  *

test/dm/core.c

@@ -1351,3 +1351,25 @@ static int dm_test_dev_get_mem(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_dev_get_mem, UTF_SCAN_FDT);
+
+/* Test uclass_try_first_device() */
+static int dm_test_try_first_device(struct unit_test_state *uts)
+{
+	struct udevice *dev;
+
+	/* Check that it doesn't create a device or uclass */
+	ut_assertnull(uclass_find(UCLASS_TEST));
+	ut_assertnull(uclass_try_first_device(UCLASS_TEST));
+	ut_assertnull(uclass_try_first_device(UCLASS_TEST));
+	ut_assertnull(uclass_find(UCLASS_TEST));
+
+	/* Create a test device */
+	ut_assertok(device_bind_by_name(uts->root, false, &driver_info_manual,
+					&dev));
+	dev = uclass_try_first_device(UCLASS_TEST);
+	ut_assertnonnull(dev);
+	ut_asserteq(UCLASS_TEST, device_get_uclass_id(dev));
+
+	return 0;
+}
+DM_TEST(dm_test_try_first_device, 0);