In file included from include/linux/skbuff.h:34:0,
from include/linux/icmpv6.h:4,
from include/linux/ipv6.h:75,
from include/net/ipv6.h:16,
from include/linux/sunrpc/clnt.h:27,
from include/linux/nfs_fs.h:30,
from fs/lockd/clntlock.c:13:
include/linux/dma-mapping.h: In function 'dma_map_resource':
>> include/linux/dma-mapping.h:274:16: warning: unused variable 'pfn' [-Wunused-variable]
unsigned long pfn = __phys_to_pfn(phys_addr);
^~~
The pfn value is only used once in the call to pfn_valid(), remove the
variable and calculate the pfn when it's needed. Note that the kbuild
report is old and PHYS_PFN() is now used instead of __phys_to_pfn() to
calculate the pfn.