Hi Christoph,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.17-rc1 next-20180416]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Christoph-Hellwig/dma-mapping-bypass-dma_ops-for-direct-mappings/20180416-230032
config: i386-defconfig (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   drivers/char/agp/intel-gtt.o: In function `intel_gmch_probe':
>> intel-gtt.c:(.text+0x11e4): undefined reference to `swiotlb_dma_ops'
   drivers/ata/ahci.o: In function `ahci_init_one':
>> ahci.c:(.text+0x108d): undefined reference to `swiotlb_dma_ops'
   drivers/net/ethernet/broadcom/bnx2.o: In function `bnx2_init_one':
>> bnx2.c:(.text+0x7fe7): undefined reference to `swiotlb_dma_ops'
   drivers/net/ethernet/broadcom/tg3.o: In function `tg3_init_one':
>> tg3.c:(.text+0x13549): undefined reference to `swiotlb_dma_ops'
   drivers/net/ethernet/intel/e1000/e1000_main.o: In function `e1000_probe':
>> e1000_main.c:(.text+0x49b3): undefined reference to `swiotlb_dma_ops'
   drivers/net/ethernet/intel/e1000e/netdev.o:netdev.c:(.text+0xa65e): more undefined references to `swiotlb_dma_ops' follow

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