mux: mmio: use reg property when parent device is not a syscon

The DT binding for the reg-mux compatible states it can be used when the
"parent device of mux controller is not syscon device". It also allows
for a reg property. When the reg property is provided, use that to
identify the address space for this mux. If not provided fallback to
using the parent device as a regmap provider.

While here use dev_err_probe() in the error path to prevent printing
a message on probe defer which now can happen in extra ways.
Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Acked-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20240104154552.17852-1-afd@ti.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mux/mmio.c

@@ -44,15 +44,20 @@ static int mux_mmio_probe(struct platform_device *pdev)
 	int ret;
 	int i;
 
-	if (of_device_is_compatible(np, "mmio-mux"))
+	if (of_device_is_compatible(np, "mmio-mux")) {
 		regmap = syscon_node_to_regmap(np->parent);
-	else
-		regmap = dev_get_regmap(dev->parent, NULL) ?: ERR_PTR(-ENODEV);
-	if (IS_ERR(regmap)) {
-		ret = PTR_ERR(regmap);
-		dev_err(dev, "failed to get regmap: %d\n", ret);
-		return ret;
+	} else {
+		regmap = device_node_to_regmap(np);
+		/* Fallback to checking the parent node on "real" errors. */
+		if (IS_ERR(regmap) && regmap != ERR_PTR(-EPROBE_DEFER)) {
+			regmap = dev_get_regmap(dev->parent, NULL);
+			if (!regmap)
+				regmap = ERR_PTR(-ENODEV);
+		}
 	}
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap),
+				     "failed to get regmap\n");
 
 	ret = of_property_count_u32_elems(np, "mux-reg-masks");
 	if (ret == 0 || ret % 2)