raspberrypi-firmware: Export the general transaction function.

raspberrypi inclusion
category: feature
bugzilla: 50432

--------------------------------

The vc4-firmware-kms module is going to be doing the MBOX FB call.
Signed-off-by: NEric Anholt <eric@anholt.net>
Signed-off-by: NFang Yafen <yafen@iscas.ac.cn>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/firmware/raspberrypi.c

@@ -43,7 +43,7 @@ static void response_callback(struct mbox_client *cl, void *msg)
  * Sends a request to the firmware through the BCM2835 mailbox driver,
  * and synchronously waits for the reply.
  */
-static int
+int
 rpi_firmware_transaction(struct rpi_firmware *fw, u32 chan, u32 data)
 {
 	u32 message = MBOX_MSG(chan, data);
@@ -68,6 +68,7 @@ rpi_firmware_transaction(struct rpi_firmware *fw, u32 chan, u32 data)
 
 	return ret;
 }
+EXPORT_SYMBOL_GPL(rpi_firmware_transaction);
 
 /**
  * rpi_firmware_property_list - Submit firmware property list