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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Tony Luck <tony.luck@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	linuxppc-dev@lists.ozlabs.org, iommu@lists.linux-foundation.org,
	linux-ia64@vger.kernel.org, Robin Murphy <robin.murphy@arm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH 08/20] powerpc/dma: remove the unused dma_nommu_ops export
Date: Thu, 23 Aug 2018 09:50:46 +1000	[thread overview]
Message-ID: <fcbf37b6f8a032713a1e07f837544be21f3567d9.camel@kernel.crashing.org> (raw)
In-Reply-To: <20180822064531.GA19284@lst.de>

On Wed, 2018-08-22 at 08:45 +0200, Christoph Hellwig wrote:
> On Thu, Aug 09, 2018 at 10:01:16AM +1000, Benjamin Herrenschmidt wrote:
> > On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote:
> > > It turns out cxl actually uses it.  So for now skip this patch,
> > > although random code in drivers messing with dma ops will need to
> > > be sorted out sooner or later.
> > 
> > CXL devices are "special", they bypass the classic iommu in favor of
> > allowing the device to operate using the main processor page tables
> > using an MMU context (so basically the device can use userspace
> > addresses directly), akin to ATS.
> > 
> > I think the code currently uses the nommu ops as a way to do a simple
> > kernel mapping for kernel drivers using CXL (not userspace stuff)
> > though.
> 
> Its still a horrible idea to have this in drivers/, we need some
> core API to mediate this behavior.  Also if the device supports
> using virtual addresses dma_nommu_ops seems wrong as it won't do
> the right thing for e.g. vmalloc addresses not mapped into the
> kernel linear mapping (which I guess can't currently happen on
> powerpc, but still..)

You are right it won't do the right thing, but neither will standard
DMA ops, will they ? Drivers know not to try to dma_map vmalloc
addresses without first getting the underlying page, nothing unusal
there.

Yes I agree having this in drivers somewhat sucks though.

Cheers,
Ben.

  reply	other threads:[~2018-08-22 23:51 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-30 16:38 use generic DMA mapping code in powerpc Christoph Hellwig
2018-07-30 16:38 ` [PATCH 01/20] kernel/dma/direct: take DMA offset into account in dma_direct_supported Christoph Hellwig
2018-08-08 23:44   ` Benjamin Herrenschmidt
2018-08-22  6:53     ` Christoph Hellwig
2018-08-22 23:59       ` Benjamin Herrenschmidt
2018-08-23  5:24         ` Christoph Hellwig
2018-08-23  5:24           ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 02/20] kernel/dma/direct: refine dma_direct_alloc zone selection Christoph Hellwig
2018-08-08 23:54   ` Benjamin Herrenschmidt
2018-08-22  6:58     ` Christoph Hellwig
2018-08-23  0:01       ` Benjamin Herrenschmidt
2018-08-23  5:26         ` Christoph Hellwig
2018-07-30 16:38 ` [PATCH 03/20] dma-mapping: make the get_required_mask method available unconditionally Christoph Hellwig
2018-07-30 16:38 ` [PATCH 04/20] ia64: remove get_required_mask implementation Christoph Hellwig
2018-07-30 16:38 ` [PATCH 05/20] swiotlb: allow the architecture to provide a get_required_mask hook Christoph Hellwig
2018-08-27 16:06   ` Konrad Rzeszutek Wilk
2018-07-30 16:38 ` [PATCH 06/20] dma-noncoherent: add an optional arch hook for ->get_required_mask Christoph Hellwig
2018-07-30 16:38 ` [PATCH 07/20] powerpc/dma: remove the unused ARCH_HAS_DMA_MMAP_COHERENT define Christoph Hellwig
2018-08-08 23:56   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 08/20] powerpc/dma: remove the unused dma_nommu_ops export Christoph Hellwig
2018-07-31 12:16   ` Christoph Hellwig
2018-08-09  0:01     ` Benjamin Herrenschmidt
2018-08-22  6:45       ` Christoph Hellwig
2018-08-22 23:50         ` Benjamin Herrenschmidt [this message]
2018-07-30 16:38 ` [PATCH 09/20] powerpc/dma: remove the unused ISA_DMA_THRESHOLD export Christoph Hellwig
2018-08-09  0:14   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 10/20] powerpc/dma-noncoherent: don't disable irqs over kmap_atomic Christoph Hellwig
2018-08-09  0:27   ` Benjamin Herrenschmidt
2018-08-22  7:02     ` Christoph Hellwig
2018-08-22 23:45       ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 11/20] powerpc/dma: split the two __dma_alloc_coherent implementations Christoph Hellwig
2018-08-09  0:40   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 12/20] powerpc/dma: use phys_to_dma instead of get_dma_offset Christoph Hellwig
2018-08-09  0:43   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 13/20] powerpc/dma: remove get_dma_offset Christoph Hellwig
2018-08-09  0:45   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 14/20] powerpc/dma: replace dma_nommu_dma_supported with dma_direct_supported Christoph Hellwig
2018-08-09  0:49   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 15/20] powerpc/dma: remove the unused unmap_page and unmap_sg methods Christoph Hellwig
2018-08-09  0:49   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 16/20] powerpc/dma: use dma_direct_{alloc,free} Christoph Hellwig
2018-08-09  0:52   ` Benjamin Herrenschmidt
2018-08-27  8:51     ` Scott Wood
2018-07-30 16:38 ` [PATCH 17/20] powerpc/dma-swiotlb: use generic swiotlb_dma_ops Christoph Hellwig
2018-08-09  0:54   ` Benjamin Herrenschmidt
2018-08-09  1:57     ` Benjamin Herrenschmidt
2018-08-22  7:04       ` Christoph Hellwig
2018-07-30 16:38 ` [PATCH 18/20] powerpc/dma-noncoherent: use generic dma_noncoherent_ops Christoph Hellwig
2018-08-09  1:00   ` Benjamin Herrenschmidt
2018-07-30 16:38 ` [PATCH 19/20] powerpc/dma: use the generic dma-direct map_page and map_sg routines Christoph Hellwig
2018-07-30 16:38 ` [PATCH 20/20] powerpc/dma: remove dma_nommu_mmap_coherent Christoph Hellwig
2018-08-09  1:05   ` Benjamin Herrenschmidt

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