From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org, linux-arch@vger.kernel.org,
linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-parisc@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Joerg Roedel <joro@8bytes.org>,
x86@kernel.org, Robin Murphy <robin.murphy@arm.com>,
linux-kernel@vger.kernel.org, Jon Mason <jdmason@kudzu.us>,
xen-devel@lists.xenproject.org,
David Woodhouse <dwmw2@infradead.org>,
linux-arm-kernel@lists.infradead.org,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: remove the ->mapping_error method from dma_map_ops V3
Date: Fri, 30 Nov 2018 18:59:20 +0000 [thread overview]
Message-ID: <20181130185920.GG30658@n2100.armlinux.org.uk> (raw)
In-Reply-To: <20181130132231.16512-1-hch@lst.de>
On Fri, Nov 30, 2018 at 02:22:08PM +0100, Christoph Hellwig wrote:
> Error reporting for the dma_map_single and dma_map_page operations is
> currently a mess. Both APIs directly return the dma_addr_t to be used for
> the DMA, with a magic error escape that is specific to the instance and
> checked by another method provided. This has a few downsides:
>
> - the error check is easily forgotten and a __must_check marker doesn't
> help as the value always is consumed anyway
> - the error checking requires another indirect call, which have gotten
> incredibly expensive
> - a lot of code is wasted on implementing these methods
>
> The historical reason for this is that people thought DMA mappings would
> not fail when the API was created, which sounds like a really bad
> assumption in retrospective, and then we tried to cram error handling
> onto it later on.
>
> There basically are two variants: the error code is 0 because the
> implementation will never return 0 as a valid DMA address, or the error
> code is all-F as the implementation won't ever return an address that
> high. The old AMD GART is the only one not falling into these two camps
> as it picks sort of a relative zero relative to where it is mapped.
>
> The 0 return doesn't work for direct mappings that have ram at address
> zero and a lot of IOMMUs that start allocating bus space from address
> zero, so we can't consolidate on that, but I think we can move everyone
> to all-Fs, which the patch here does. The reason for that is that
> there is only one way to ever get this address: by doing a 1-byte long,
> 1-byte aligned mapping, but all our mappings are not only longer but
> generally aligned, and the mappings have to keep at least the basic
> alignment.
>
> A git tree is also available here:
>
> git://git.infradead.org/users/hch/misc.git dma-mapping-error.3
Hi Chris,
For patches 1, 3 and 23,
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Thanks.
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up
next prev parent reply other threads:[~2018-11-30 18:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-30 13:22 remove the ->mapping_error method from dma_map_ops V3 Christoph Hellwig
2018-11-30 13:22 ` [PATCH 01/23] dma-mapping: provide a generic DMA_MAPPING_ERROR Christoph Hellwig
2018-12-04 16:41 ` Robin Murphy
2018-12-04 22:33 ` Christoph Hellwig
2018-11-30 13:22 ` [PATCH 02/23] dma-direct: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-30 13:22 ` [PATCH 03/23] arm: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 04/23] powerpc/iommu: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 05/23] mips/jazz: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 06/23] s390: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 07/23] sparc: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 08/23] parisc/ccio: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 09/23] parisc/sba_iommu: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 10/23] arm64: remove the dummy_dma_ops mapping_error method Christoph Hellwig
2018-11-30 13:22 ` [PATCH 11/23] alpha: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-30 13:22 ` [PATCH 12/23] ia64/sba_iommu: improve internal map_page users Christoph Hellwig
2018-11-30 13:22 ` [PATCH 13/23] ia64/sba_iommu: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-30 13:22 ` [PATCH 14/23] ia64/sn: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 15/23] x86/amd_gart: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 16/23] x86/calgary: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 17/23] iommu: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 18/23] iommu/intel: small map_page cleanup Christoph Hellwig
2018-11-30 13:22 ` [PATCH 19/23] iommu/vt-d: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-30 13:22 ` [PATCH 20/23] iommu/dma-iommu: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 21/23] xen-swiotlb: " Christoph Hellwig
2018-12-02 12:42 ` Konrad Rzeszutek Wilk
2018-11-30 13:22 ` [PATCH 22/23] dma-mapping: " Christoph Hellwig
2018-11-30 13:22 ` [PATCH 23/23] dma-mapping: return an error code from dma_mapping_error Christoph Hellwig
2018-11-30 18:59 ` Russell King - ARM Linux [this message]
2018-11-30 19:43 ` remove the ->mapping_error method from dma_map_ops V3 Linus Torvalds
2018-12-03 17:27 ` Christoph Hellwig
2018-12-06 14:57 ` Christoph Hellwig
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181130185920.GG30658@n2100.armlinux.org.uk \
--to=linux@armlinux.org.uk \
--cc=dwmw2@infradead.org \
--cc=hch@lst.de \
--cc=iommu@lists.linux-foundation.org \
--cc=jdmason@kudzu.us \
--cc=joro@8bytes.org \
--cc=linux-alpha@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-ia64@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-parisc@vger.kernel.org \
--cc=m.szyprowski@samsung.com \
--cc=robin.murphy@arm.com \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).