[kbuild-all] Re: drivers/media/pci/intel/ipu3/ipu3-cio2.c:163:56: warning: implicit conversion from 'unsigned long' to 'u16' (aka 'unsigned short') changes value from 131072 to 0

On Sat, Nov 21, 2020 at 04:23:05PM +0800, kernel test robot wrote: > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > head: 27bba9c532a8d21050b94224ffd310ad0058c353 > commit: 7b285f41f7376dc37e7fad1e803995fd39f42848 media: ipu3-cio2: Introduce CIO2_LOP_ENTRIES constant > date: 2 months ago > config: arm64-randconfig-r031-20201121 (attached as .config) > compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project bec968cbb367dd03439c89c1d4ef968ef662d7c0) > reproduce (this is a W=1 build): > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # install arm64 cross compiling tool for clang build > # apt-get install binutils-aarch64-linux-gnu > # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit... > git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git > git fetch --no-tags linus master > git checkout 7b285f41f7376dc37e7fad1e803995fd39f42848 > # save the attached .config to linux build tree > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm64 > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kernel test robot <lkp(a)intel.com&gt; > > All warnings (new ones prefixed by >>): > > >> drivers/media/pci/intel/ipu3/ipu3-cio2.c:163:56: warning: implicit conversion from 'unsigned long' to 'u16' (aka 'unsigned short') changes value from 131072 to 0 [-Wconstant-conversion] > entry[1].second_entry.num_of_pages = CIO2_LOP_ENTRIES * CIO2_MAX_LOPS; > ~ ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~ > 1 warning generated. Okay, now we have an interesting case. The IP is quite unlikely be used on ARM64, but my patches made the clear picture about use of PAGE_SIZE here. So, I see at least the following options to mitigate the above, i.e.: 1/ reduce driver scope to X86 2/ fix the variables to be wider type to be able to hold PAGE_SIZE > 4k 3/ switch to custom PAGE_SIZE / _SHIFT / _MASK and accompanying macros And I still consider 3/ is silly move because as we see the driver was never assumed to work with big page sizes (besides unsigned short type here, PAGE_SHIFT and PAGE_MASK in the original code was as is and on ARM64 they compiled to 0 values w/o warnings, effectively make the driver improperly functioning anyway).