lib: utils/regmap: Add simple FDT based regmap framework

We add a simple FDT based regmap framework which is built on top of
generic regmap library. The phandle of FDT regmap DT node is treated
as unique regmap ID. The FDT based regmap drivers will be probed
on-demand from fdt_regmap_get_by_phandle() and fdt_regmap_get()
called by the regmap client drivers.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>

lib/utils/regmap/fdt_regmap.c

@@ -0,0 +1,94 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2023 Ventana Micro Systems Inc.
+ *
+ * Authors:
+ *   Anup Patel <apatel@ventanamicro.com>
+ */
+
+#include <libfdt.h>
+#include <sbi/sbi_error.h>
+#include <sbi_utils/fdt/fdt_helper.h>
+#include <sbi_utils/regmap/fdt_regmap.h>
+
+/* List of FDT regmap drivers generated at compile time */
+extern struct fdt_regmap *fdt_regmap_drivers[];
+extern unsigned long fdt_regmap_drivers_size;
+
+static int fdt_regmap_init(void *fdt, int nodeoff, u32 phandle)
+{
+	int pos, rc;
+	struct fdt_regmap *drv;
+	const struct fdt_match *match;
+
+	/* Try all I2C drivers one-by-one */
+	for (pos = 0; pos < fdt_regmap_drivers_size; pos++) {
+		drv = fdt_regmap_drivers[pos];
+		match = fdt_match_node(fdt, nodeoff, drv->match_table);
+		if (match && drv->init) {
+			rc = drv->init(fdt, nodeoff, phandle, match);
+			if (rc == SBI_ENODEV)
+				continue;
+			if (rc)
+				return rc;
+			return 0;
+		}
+	}
+
+	return SBI_ENOSYS;
+}
+
+static int fdt_regmap_find(void *fdt, int nodeoff, u32 phandle,
+			   struct regmap **out_rmap)
+{
+	int rc;
+	struct regmap *rmap = regmap_find(phandle);
+
+	if (!rmap) {
+		/* Regmap not found so initialize matching driver */
+		rc = fdt_regmap_init(fdt, nodeoff, phandle);
+		if (rc)
+			return rc;
+
+		/* Try to find regmap again */
+		rmap = regmap_find(phandle);
+		if (!rmap)
+			return SBI_ENOSYS;
+	}
+
+	if (out_rmap)
+		*out_rmap = rmap;
+
+	return 0;
+}
+
+int fdt_regmap_get_by_phandle(void *fdt, u32 phandle,
+			      struct regmap **out_rmap)
+{
+	int pnodeoff;
+
+	if (!fdt || !out_rmap)
+		return SBI_EINVAL;
+
+	pnodeoff = fdt_node_offset_by_phandle(fdt, phandle);
+	if (pnodeoff < 0)
+		return pnodeoff;
+
+	return fdt_regmap_find(fdt, pnodeoff, phandle, out_rmap);
+}
+
+int fdt_regmap_get(void *fdt, int nodeoff, struct regmap **out_rmap)
+{
+	int len;
+	const fdt32_t *val;
+
+	if (!fdt || (nodeoff < 0) || !out_rmap)
+		return SBI_EINVAL;
+
+	val = fdt_getprop(fdt, nodeoff, "regmap", &len);
+	if (!val)
+		return SBI_ENOENT;
+
+	return fdt_regmap_get_by_phandle(fdt, fdt32_to_cpu(*val), out_rmap);
+}