regulator: fixed: support deferred probe for DT GPIOs

of_get_named_gpio() needs the driver hosting the GPIO that the DT
property references to have been probed. Detect this specific failure,
and defer the probe of the whole regulator until this API can complete.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/fixed.c

@@ -61,11 +61,11 @@ of_get_fixed_voltage_config(struct device *dev)
 	config = devm_kzalloc(dev, sizeof(struct fixed_voltage_config),
 								 GFP_KERNEL);
 	if (!config)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	config->init_data = of_get_regulator_init_data(dev, dev->of_node);
 	if (!config->init_data)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
 	init_data = config->init_data;
 	init_data->constraints.apply_uV = 0;
@@ -76,13 +76,26 @@ of_get_fixed_voltage_config(struct device *dev)
 	} else {
 		dev_err(dev,
 			 "Fixed regulator specified with variable voltages\n");
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	if (init_data->constraints.boot_on)
 		config->enabled_at_boot = true;
 
 	config->gpio = of_get_named_gpio(np, "gpio", 0);
+	/*
+	 * of_get_named_gpio() currently returns ENODEV rather than
+	 * EPROBE_DEFER. This code attempts to be compatible with both
+	 * for now; the ENODEV check can be removed once the API is fixed.
+	 * of_get_named_gpio() doesn't differentiate between a missing
+	 * property (which would be fine here, since the GPIO is optional)
+	 * and some other error. Patches have been posted for both issues.
+	 * Once they are check in, we should replace this with:
+	 * if (config->gpio < 0 && config->gpio != -ENOENT)
+	 */
+	if ((config->gpio == -ENODEV) || (config->gpio == -EPROBE_DEFER))
+		return ERR_PTR(-EPROBE_DEFER);
+
 	delay = of_get_property(np, "startup-delay-us", NULL);
 	if (delay)
 		config->startup_delay = be32_to_cpu(*delay);
@@ -172,10 +185,13 @@ static int __devinit reg_fixed_voltage_probe(struct platform_device *pdev)
 	struct regulator_config cfg = { };
 	int ret;
 
-	if (pdev->dev.of_node)
+	if (pdev->dev.of_node) {
 		config = of_get_fixed_voltage_config(&pdev->dev);
-	else
+		if (IS_ERR(config))
+			return PTR_ERR(config);
+	} else {
 		config = pdev->dev.platform_data;
+	}
 
 	if (!config)
 		return -ENOMEM;