[PATCH v2 1/2] firewire: Simplify storing pointers in device id struct

[Uwe Kleine-König (The Capable Hub)]

Technically it is fine (on all current Linux architectures) to store a
pointer in an unsigned long variable. However this needs explicit
casting which is an easy source for type mismatches.

By replacing the plain unsigned long .driver_data in struct
ieee1394_device_id by an anonymous union, most of the casting can be
dropped. There is still some implicit casting involved (between a void *
and a driver specific pointer type), but that's better than the approach
to store a pointer in an unsigned long variable as this doesn't lose the
information that the data being pointed to is const.

This also helps the porting effort to let Linux support CHERI where an
unsigned long is unsuitable to hold a pointer.

All users of struct ieee1394_device_id are initialized in a way that is
compatible with the new definition, so no adaptions are needed there.

Signed-off-by: Uwe Kleine-König (The Capable Hub) <u.kleine-koenig@xxxxxxxxxxxx>
---
 include/linux/mod_devicetable.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 23ff24080dfd..3b0c9a251a2e 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -61,7 +61,10 @@ struct ieee1394_device_id {
 	__u32 model_id;
 	__u32 specifier_id;
 	__u32 version;
-	kernel_ulong_t driver_data;
+	union {
+		kernel_ulong_t driver_data;
+		const void *driver_data_ptr;
+	};
 };
 
 
-- 
2.47.3