[PATCH/RFC] soc: bcm2835: Make !RASPBERRYPI_FIRMWARE dummies return failure

[geert@linux-m68k.org (Geert Uytterhoeven)]

If CONFIG_RASPBERRYPI_FIRMWARE=n:

    drivers/gpio/gpio-raspberrypi-exp.c: In function ?rpi_exp_gpio_get_polarity?:
    drivers/gpio/gpio-raspberrypi-exp.c:71: warning: ?get.polarity? is used uninitialized in this function
    drivers/gpio/gpio-raspberrypi-exp.c: In function ?rpi_exp_gpio_get_direction?:
    drivers/gpio/gpio-raspberrypi-exp.c:150: warning: ?get.direction? is used uninitialized in this function

The dummy firmware interface functions return 0, which means success,
causing subsequent code to make use of the never initialized output
parameter.

Fix this by making the dummy functions return an error code (-ENOSYS)
instead.

Note that this assumes the firmware always fills in the requested data
in the CONFIG_RASPBERRYPI_FIRMWARE=y case.

Fixes: d45f1a563b92dac7 ("staging: vc04_services: fix up rpi firmware functions")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Should get.polarity resp. get.direction be preinitialized instead,
like is done for get.state?

static int rpi_exp_gpio_get(struct gpio_chip *gc, unsigned int off)
{
        ...
        get.state = 0;          /* storage for returned value */

        ret = rpi_firmware_property(gpio->fw, RPI_FIRMWARE_GET_GPIO_STATE,
                                         &get, sizeof(get));
        ...
}

This would avoid returning uninitialized data if the firmware did not
fill in the requested data.
---
 include/soc/bcm2835/raspberrypi-firmware.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
index 50df5b28d2c9df6e..8ee8991aa099af3a 100644
--- a/include/soc/bcm2835/raspberrypi-firmware.h
+++ b/include/soc/bcm2835/raspberrypi-firmware.h
@@ -143,13 +143,13 @@ struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
 static inline int rpi_firmware_property(struct rpi_firmware *fw, u32 tag,
 					void *data, size_t len)
 {
-	return 0;
+	return -ENOSYS;
 }
 
 static inline int rpi_firmware_property_list(struct rpi_firmware *fw,
 					     void *data, size_t tag_size)
 {
-	return 0;
+	return -ENOSYS;
 }
 
 static inline struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
-- 
2.7.4