Hi Pekka,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.8-rc5 next-20200714]
[cannot apply to mmotm/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use  as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Pekka-Enberg/mm-pgtable-Make-generic-pgprot_-macros-available-for-no-MMU/20200714-180502
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 0dc589da873b58b70f4caf4b070fb0cf70fdd1dc
config: arm-randconfig-r033-20200714 (attached as .config)
compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0
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
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   In file included from include/linux/mm.h:32,
                    from include/linux/scatterlist.h:8,
                    from include/linux/dma-mapping.h:11,
                    from drivers/gpu/drm/tilcdc/tilcdc_crtc.c:8:
   include/linux/pgtable.h: In function 'pgprot_modify':
>> include/linux/pgtable.h:834:26: error: self-comparison always evaluates to true [-Werror=tautological-compare]
     834 |  if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
         |                          ^~
   include/linux/pgtable.h:836:26: error: self-comparison always evaluates to true [-Werror=tautological-compare]
     836 |  if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
         |                          ^~
   include/linux/pgtable.h:838:26: error: self-comparison always evaluates to true [-Werror=tautological-compare]
     838 |  if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
         |                          ^~
   cc1: all warnings being treated as errors

vim +834 include/linux/pgtable.h

   829	
   830	#ifndef pgprot_modify
   831	#define pgprot_modify pgprot_modify
   832	static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
   833	{
 > 834		if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
   835			newprot = pgprot_noncached(newprot);
   836		if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
   837			newprot = pgprot_writecombine(newprot);
   838		if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
   839			newprot = pgprot_device(newprot);
   840		return newprot;
   841	}
   842	#endif
   843	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org