iwlwifi problem with iommu/intel-iommu: Enable CONFIG_DMA_DIRECT_OPS=y and clean up intel_{alloc,free}_coherent()

[Fabio Coatti <fabio.coatti@gmail.com>]

Hi all,
since kernel 4.17  my laptop fails to enable wireless card (04:00.0 Network 
controller: Intel Corporation Wireless 8260 (rev 3a) )
with this error:

Jul 01 09:34:36 hobbes kernel: iwlwifi: probe of 0000:04:00.0 failed with error 
-12

I bisected the issue to this result:
d657c5c73ca987214a6f9436e435b34fc60f332a is the first bad commit
commit d657c5c73ca987214a6f9436e435b34fc60f332a
Author: Christoph Hellwig <hch@lst.de>
Date:   Mon Mar 19 11:38:20 2018 +0100

    iommu/intel-iommu: Enable CONFIG_DMA_DIRECT_OPS=y and clean up 
intel_{alloc,free}_coherent()
    
    Use the dma_direct_*() helpers and clean up the code flow.
    
    Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Joerg Roedel <joro@8bytes.org>
    Cc: Jon Mason <jdmason@kudzu.us>
    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Muli Ben-Yehuda <mulix@mulix.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: iommu@lists.linux-foundation.org
    Link: http://lkml.kernel.org/r/20180319103826.12853-9-hch@lst.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>

:040000 040000 9b907b7d761c6121d603c649421749ffd4e13999 
2f396bd9e11c46e865a46107cd3cc9ef6f9ee6dd M      drivers


By reverting this commit the card works again, tested in 4.17.3 . I've noticed 
that the corresponding amd commit ( b468620f2a1dfdcfddfd6fa54367b8bcc1b51248)
has been reverted in linus tree (e16c4790de39dc861b749674c2a9319507f6f64f), 
and 4.16.X stable tree iirc,  but the intel one has not been reverted.

hw: Lenovo P50 Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz

Please let me know if more details are needed, but CC: me as I'm not currently 
subscribed to LKML.

many thanks.