drivers/mtd_default: add helper function for default MTD devices

drivers/include/mtd_default.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2023 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+/**
+ * @ingroup     drivers_mtd
+ * @{
+ * @brief       Default MTD device configuration
+ *
+ * Helpers for generic MTD use.
+ *
+ * @author      Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ */
+#ifndef MTD_DEFAULT_H
+#define MTD_DEFAULT_H
+
+#include "board.h"
+#include "mtd.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief   Number of MTD devices
+ */
+#ifndef MTD_NUMOF
+#if defined(MTD_3)
+#define MTD_NUMOF 4
+#elif defined(MTD_2)
+#define MTD_NUMOF 3
+#elif defined(MTD_1)
+#define MTD_NUMOF 2
+#elif defined(MTD_0)
+#define MTD_NUMOF 1
+#else
+#define MTD_NUMOF 0
+#endif
+#endif
+
+/**
+ * @brief   Get the default MTD device by index
+ *
+ * @param[in] idx   Index of the MTD device
+ *
+ * @return  MTD_0 for @p idx 0 and so on
+ *          NULL if no MTD device exists for the given index
+ */
+static inline mtd_dev_t *mtd_default_get_dev(unsigned idx)
+{
+    switch (idx) {
+#ifdef MTD_0
+    case 0: return MTD_0;
+#endif
+#ifdef MTD_1
+    case 1: return MTD_1;
+#endif
+#ifdef MTD_2
+    case 2: return MTD_2;
+#endif
+#ifdef MTD_3
+    case 3: return MTD_3;
+#endif
+    }
+
+    return NULL;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MTD_DEFAULT_H */
+/** @} */