gpio: fix probe() error return in gpio driver probes

A number of drivers in drivers/gpio return -ENODEV when confronted with
missing setup parameters such as the platform data. However, returning
-ENODEV causes the driver layer to silently ignore the driver as it
assumes the probe did not find anything and was only speculative.

To make life easier to discern why a driver is not being attached, change
to returning -EINVAL, which is a better description of the fact that the
driver data was not valid.

Also add a set of dev_dbg() statements to the error paths to provide an
better explanation of the error as there may be more that one point in the
driver.

Signed-off-by: Ben Dooks <[e-mail]>
Cc: David Brownell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/gpio/max7301.c

···
 	int i, ret;
 
 	pdata = spi->dev.platform_data;
-	if (!pdata || !pdata->base)
-		return -ENODEV;
+	if (!pdata || !pdata->base) {
+		dev_dbg(&spi->dev, "incorrect or missing platform data\n");
+		return -EINVAL;
+	}
 
 	/*
 	 * bits_per_word cannot be configured in platform data

drivers/gpio/max732x.c

···
 	int ret, nr_port;
 
 	pdata = client->dev.platform_data;
-	if (pdata == NULL)
-		return -ENODEV;
+	if (pdata == NULL) {
+		dev_dbg(&client->dev, "no platform data\n");
+		return -EINVAL;
+	}
 
 	chip = kzalloc(sizeof(struct max732x_chip), GFP_KERNEL);
 	if (chip == NULL)

drivers/gpio/mcp23s08.c

···
 	unsigned			base;
 
 	pdata = spi->dev.platform_data;
-	if (!pdata || !gpio_is_valid(pdata->base))
-		return -ENODEV;
+	if (!pdata || !gpio_is_valid(pdata->base)) {
+		dev_dbg(&spi->dev, "invalid or missing platform data\n");
+		return -EINVAL;
+	}
 
 	for (addr = 0; addr < 4; addr++) {
 		if (!pdata->chip[addr].is_present)

drivers/gpio/pca953x.c

···
 	int ret;
 
 	pdata = client->dev.platform_data;
-	if (pdata == NULL)
-		return -ENODEV;
+	if (pdata == NULL) {
+		dev_dbg(&client->dev, "no platform data\n");
+		return -EINVAL;
+	}
 
 	chip = kzalloc(sizeof(struct pca953x_chip), GFP_KERNEL);
 	if (chip == NULL)

drivers/gpio/pcf857x.c

···
 	int				status;
 
 	pdata = client->dev.platform_data;
-	if (!pdata)
-		return -ENODEV;
+	if (!pdata) {
+		dev_dbg(&client->dev, "no platform data\n");
+		return -EINVAL;
+	}
 
 	/* Allocate, initialize, and register this gpio_chip. */
 	gpio = kzalloc(sizeof *gpio, GFP_KERNEL);
···
 		else
 			status = i2c_read_le16(client);
 
-	} else
-		status = -ENODEV;
+	} else {
+		dev_dbg(&client->dev, "unsupported number of gpios\n");
+		status = -EINVAL;
+	}
 
 	if (status < 0)
 		goto fail;