Here are a few tips and scripts how to find unnecessary (void*) conversions.
Find (void*) functions
Here's a script that finds all functions returning (void*): find_voidp_funcs.pl
Finding and removing type conversion on such assignments
Another script has an embedded list of such function names (after the _END_), or can take such names on the commandline: type-convs.pl
./type-convs.pl linux-2.6.git kmalloc
The output is a patch that removes these type conversions; the source files are kept unchanged.
(void*) variable assignments
Some kernel structures have variables meant to be private to some driver, normally named "priv" or "private"; these are of type "(void *)", and need not be casted to some other type.
This script returns a patch for such assignments: voidp_vars.pl
./voidp_vars.pl linux-2.6.git kmalloc