Hi Daniel,

I love your patch! Perhaps something to improve:

[auto build test WARNING on next-20210115]
[also build test WARNING on v5.11-rc3]
[cannot apply to tegra-drm/drm/tegra/for-next linus/master v5.11-rc3 v5.11-rc2 v5.11-rc1]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Daniel-Vetter/drm-buf-Add-debug-option/20210115-210650
base:    b3a3cbdec55b090d22a09f75efb7c7d34cb97f25
config: i386-randconfig-a012-20210115 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/a0f2603f574f0a1aedd7719cbb47b807796d2367
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Daniel-Vetter/drm-buf-Add-debug-option/20210115-210650
        git checkout a0f2603f574f0a1aedd7719cbb47b807796d2367
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

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

All warnings (new ones prefixed by >>):

   drivers/dma-buf/dma-buf.c: In function '__map_dma_buf':
>> drivers/dma-buf/dma-buf.c:676:5: warning: "CONFIG_DMABUF_DEBUG" is not defined, evaluates to 0 [-Wundef]
     676 | #if CONFIG_DMABUF_DEBUG
         |     ^~~~~~~~~~~~~~~~~~~
   drivers/dma-buf/dma-buf.c: In function '__unmap_dma_buf':
   drivers/dma-buf/dma-buf.c:816:5: warning: "CONFIG_DMABUF_DEBUG" is not defined, evaluates to 0 [-Wundef]
     816 | #if CONFIG_DMABUF_DEBUG
         |     ^~~~~~~~~~~~~~~~~~~


vim +/CONFIG_DMABUF_DEBUG +676 drivers/dma-buf/dma-buf.c

   668	
   669	static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
   670					       enum dma_data_direction direction)
   671	{
   672		struct sg_table *sg_table;
   673	
   674		sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
   675	
 > 676	#if CONFIG_DMABUF_DEBUG
   677		if (sg_table) {
   678			int i;
   679			struct scatterlist *sg;
   680	
   681			/* To catch abuse of the underlying struct page by importers mix
   682			 * up the bits, but take care to preserve the low SG_ bits to
   683			 * not corrupt the sgt. The mixing is undone in __unmap_dma_buf
   684			 * before passing the sgt back to the exporter. */
   685			for_each_sgtable_sg(sg_table, sg, i)
   686				sg->page_link ^= ~0xffUL;
   687		}
   688	#endif
   689	
   690		return sg_table;
   691	}
   692	

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