From: Christoph Hellwig <hch@lst.de>
To: Tomasz Figa <tfiga@chromium.org>
Cc: Christoph Hellwig <hch@lst.de>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
Joonyoung Shim <jy0922.shim@samsung.com>,
Seung-Woo Kim <sw0312.kim@samsung.com>,
Kyungmin Park <kyungmin.park@samsung.com>,
Ben Skeggs <bskeggs@redhat.com>, Pawel Osciak <pawel@osciak.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Matt Porter <mporter@kernel.crashing.org>,
"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
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<iommu@lists.linux-foundation.org>,
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"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
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<linux-arm-kernel@lists.infradead.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>
Subject: Re: [PATCH 19/28] dma-mapping: replace DMA_ATTR_NON_CONSISTENT with dma_{alloc, free}_pages
Date: Thu, 20 Aug 2020 07:15:12 +0200 [thread overview]
Message-ID: <20200820051512.GA5141@lst.de> (raw)
In-Reply-To: <CAAFQd5Bbp-eAVKS1MKS8xtrT4ZoOmBPfZyw9mys=eOmDb6r8Lw@mail.gmail.com>
On Wed, Aug 19, 2020 at 05:03:52PM +0200, Tomasz Figa wrote:
> >
> > -Warning: These pieces of the DMA API should not be used in the
> > -majority of cases, since they cater for unlikely corner cases that
> > -don't belong in usual drivers.
> > +These APIs allow to allocate pages that can be used like normal pages
> > +in the kernel direct mapping, but are guaranteed to be DMA addressable.
>
> Could we elaborate a bit more on what "like normal pages in kernel
> direct mapping" mean from the driver perspective?
It mostly means you can call virt_to_page and then do anything you'd
do with a page struct. Unlike dma_alloc_attrs that just return an
opaque virtual address that the caller is not allowed to poke into.
> There is one aspect that the existing dma_alloc_attrs() handles, but
> this new function doesn't: IOMMU support. The function will always
> allocate a physically-contiguous block memory, which is a costly
> operation and not even guaranteed to succeed, even if enough free
> memory is available.
>
> Modern SoCs employ IOMMUs to avoid the need to allocate
> physically-contiguous memory and those happen to be also the devices
> that could benefit from non-coherent allocations a lot. One of the
> tasks of the DMA API was making it possible to allocate suitable
> memory for a given device, without having the driver know about the
> SoC integration details, such as the presence of an IOMMU.
This is completely out of scope for this API exactly because it
guarantees a page in the direct mapping. But see my previous mail
in reply to Robin on how you can implement the funtionality you
want right now without any help from the dma-mapping subsystem.
next prev parent reply other threads:[~2020-08-20 5:15 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200819065610eucas1p2fde88e81917071b1888e7cc01ba0f298@eucas1p2.samsung.com>
2020-08-19 6:55 ` a saner API for allocating DMA addressable pages Christoph Hellwig
2020-08-19 6:55 ` [PATCH 01/28] mm: turn alloc_pages into an inline function Christoph Hellwig
2020-08-19 6:55 ` [PATCH 02/28] drm/exynos: stop setting DMA_ATTR_NON_CONSISTENT Christoph Hellwig
2020-08-19 6:55 ` [PATCH 03/28] drm/nouveau/gk20a: " Christoph Hellwig
2020-08-19 6:55 ` [PATCH 04/28] net/au1000-eth: stop using DMA_ATTR_NON_CONSISTENT Christoph Hellwig
2020-08-19 6:55 ` [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT Christoph Hellwig
2020-08-19 11:16 ` Tomasz Figa
2020-08-19 11:51 ` Robin Murphy
2020-08-19 12:49 ` Tomasz Figa
2020-08-19 13:57 ` Christoph Hellwig
2020-08-19 14:11 ` Tomasz Figa
2020-08-20 4:45 ` Christoph Hellwig
2020-08-20 10:09 ` Tomasz Figa
2020-08-20 16:51 ` Christoph Hellwig
2020-08-19 14:07 ` Robin Murphy
2020-08-19 14:22 ` Tomasz Figa
2020-08-20 4:52 ` Christoph Hellwig
2020-08-20 5:02 ` Christoph Hellwig
2020-08-20 10:24 ` Tomasz Figa
2020-08-20 16:52 ` Christoph Hellwig
2020-08-20 17:41 ` Tomasz Figa
2020-08-19 13:54 ` Christoph Hellwig
2020-08-19 13:57 ` Tomasz Figa
2020-08-20 4:43 ` Christoph Hellwig
2020-08-20 5:20 ` Christoph Hellwig
2020-08-20 10:05 ` Tomasz Figa
2020-08-20 16:54 ` Christoph Hellwig
2020-08-20 17:33 ` Tomasz Figa
2020-09-01 11:06 ` Christoph Hellwig
2020-09-01 15:02 ` Tomasz Figa
2020-09-08 21:58 ` Tomasz Figa
2020-09-08 22:09 ` Tomasz Figa
2020-09-10 9:49 ` Sergey Senozhatsky
2020-09-10 9:57 ` Hans Verkuil
2020-09-10 10:14 ` Sergey Senozhatsky
2020-09-10 10:23 ` Hans Verkuil
2020-09-10 14:48 ` Sergey Senozhatsky
2020-09-10 15:38 ` Sergey Senozhatsky
2020-08-19 6:55 ` [PATCH 06/28] lib82596: move DMA allocation into the callers of i82596_probe Christoph Hellwig
2020-09-01 13:29 ` Thomas Bogendoerfer
2020-08-19 6:55 ` [PATCH 07/28] 53c700: improve non-coherent DMA handling Christoph Hellwig
2020-09-01 14:52 ` James Bottomley
2020-09-01 15:05 ` Matthew Wilcox
2020-09-01 15:22 ` James Bottomley
2020-09-01 16:21 ` Helge Deller
2020-09-01 16:41 ` Helge Deller
2020-09-01 16:53 ` Matthew Wilcox
2020-09-02 15:00 ` Helge Deller
2020-08-19 6:55 ` [PATCH 08/28] MIPS: make dma_sync_*_for_cpu a little less overzealous Christoph Hellwig
2020-09-01 13:53 ` Thomas Bogendoerfer
2020-08-19 6:55 ` [PATCH 09/28] MIPS/jazzdma: remove the unused vdma_remap function Christoph Hellwig
2020-09-01 13:49 ` Thomas Bogendoerfer
2020-08-19 6:55 ` [PATCH 10/28] MIPS/jazzdma: decouple from dma-direct Christoph Hellwig
2020-09-01 13:49 ` Thomas Bogendoerfer
2020-08-19 6:55 ` [PATCH 11/28] dma-mapping: add (back) arch_dma_mark_clean for ia64 Christoph Hellwig
2020-08-19 6:55 ` [PATCH 12/28] dma-direct: remove dma_direct_{alloc,free}_pages Christoph Hellwig
2020-08-19 6:55 ` [PATCH 13/28] dma-direct: lift gfp_t manipulation out of__dma_direct_alloc_pages Christoph Hellwig
2020-08-19 6:55 ` [PATCH 14/28] dma-direct: use phys_to_dma_direct in dma_direct_alloc Christoph Hellwig
2020-08-19 6:55 ` [PATCH 15/28] dma-direct: remove __dma_to_phys Christoph Hellwig
2020-08-19 6:55 ` [PATCH 16/28] dma-direct: rename and cleanup __phys_to_dma Christoph Hellwig
2020-08-19 6:55 ` [PATCH 17/28] dma-mapping: move dma_common_{mmap,get_sgtable} out of mapping.c Christoph Hellwig
2020-08-19 6:55 ` [PATCH 18/28] dma-mapping: move the dma_declare_coherent_memory documentation Christoph Hellwig
2020-08-19 6:55 ` [PATCH 19/28] dma-mapping: replace DMA_ATTR_NON_CONSISTENT with dma_{alloc,free}_pages Christoph Hellwig
2020-08-19 15:03 ` [PATCH 19/28] dma-mapping: replace DMA_ATTR_NON_CONSISTENT with dma_{alloc, free}_pages Tomasz Figa
2020-08-20 5:15 ` Christoph Hellwig [this message]
2020-08-19 6:55 ` [PATCH 20/28] sgiwd93: convert from dma_cache_sync to dma_sync_single_for_device Christoph Hellwig
2020-08-19 6:55 ` [PATCH 21/28] hal2: " Christoph Hellwig
2020-08-19 6:55 ` [PATCH 22/28] sgiseeq: " Christoph Hellwig
2020-09-01 15:22 ` Thomas Bogendoerfer
2020-09-01 17:12 ` Thomas Bogendoerfer
2020-09-01 17:16 ` Christoph Hellwig
2020-09-01 17:38 ` Thomas Bogendoerfer
2020-09-02 21:38 ` Thomas Bogendoerfer
2020-09-03 8:42 ` Christoph Hellwig
2020-09-03 8:43 ` Christoph Hellwig
2020-09-03 8:46 ` Christoph Hellwig
2020-08-19 6:55 ` [PATCH 23/28] lib82596: " Christoph Hellwig
2020-08-19 6:55 ` [PATCH 24/28] 53c700: " Christoph Hellwig
2020-08-19 6:55 ` [PATCH 25/28] dma-mapping: remove dma_cache_sync Christoph Hellwig
2020-08-19 6:55 ` [PATCH 26/28] dmapool: add dma_alloc_pages support Christoph Hellwig
2020-08-19 6:55 ` [PATCH 27/28] nvme-pci: fix PRP pool size Christoph Hellwig
2020-08-19 6:55 ` [PATCH 28/28] nvme-pci: use dma_alloc_pages backed dmapools Christoph Hellwig
2020-08-25 11:30 ` a saner API for allocating DMA addressable pages Marek Szyprowski
2020-08-25 13:26 ` Christoph Hellwig
2020-08-29 9:46 ` Helge Deller
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