[PATCH][next] firewire: cdev: Fix function cast error

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Fix the following function cast error when building with
-Wcast-function-type:

drivers/firewire/core-cdev.c: In function ‘ioctl_create_iso_context’:
drivers/firewire/core-cdev.c:985:8: error: cast between incompatible function types from ‘void (*)(struct fw_iso_context *, dma_addr_t,  void *)’ {aka ‘void (*)(struct fw_iso_context *, long long unsigned int,  void *)’} to ‘void (*)(struct fw_iso_context *, u32,  size_t,  void *, void *)’ {aka ‘void (*)(struct fw_iso_context *, unsigned int,  long unsigned int,  void *, void *)’} [-Werror=cast-function-type]
  985 |   cb = (fw_iso_callback_t)iso_mc_callback;
      |        ^
cc1: all warnings being treated as errors

This helps with the ongoing efforts to globally enable -Wcast-function-type,
so when Control Flow Integrity checking lands in the kernel, incompatible
function type casting doesn't interfere with it.

Link: https://github.com/KSPP/linux/issues/20
Link: https://github.com/KSPP/linux/issues/102
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/firewire/core-cdev.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index fb6c651214f3..fd2923599667 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -957,7 +957,10 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
 {
 	struct fw_cdev_create_iso_context *a = &arg->create_iso_context;
 	struct fw_iso_context *context;
-	fw_iso_callback_t cb;
+	union callback {
+		fw_iso_callback_t sc;
+		fw_iso_mc_callback_t mc;
+	} cb;
 	int ret;
 
 	BUILD_BUG_ON(FW_CDEV_ISO_CONTEXT_TRANSMIT != FW_ISO_CONTEXT_TRANSMIT ||
@@ -970,7 +973,7 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
 		if (a->speed > SCODE_3200 || a->channel > 63)
 			return -EINVAL;
 
-		cb = iso_callback;
+		cb.sc = iso_callback;
 		break;
 
 	case FW_ISO_CONTEXT_RECEIVE:
@@ -978,11 +981,11 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
 		    a->channel > 63)
 			return -EINVAL;
 
-		cb = iso_callback;
+		cb.sc = iso_callback;
 		break;
 
 	case FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL:
-		cb = (fw_iso_callback_t)iso_mc_callback;
+		cb.mc = iso_mc_callback;
 		break;
 
 	default:
@@ -990,7 +993,7 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
 	}
 
 	context = fw_iso_context_create(client->device->card, a->type,
-			a->channel, a->speed, a->header_size, cb, client);
+			a->channel, a->speed, a->header_size, cb.sc, client);
 	if (IS_ERR(context))
 		return PTR_ERR(context);
 	if (client->version < FW_CDEV_VERSION_AUTO_FLUSH_ISO_OVERFLOW)
-- 
2.27.0