From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>,
linux-arch@vger.kernel.org, linux-alpha@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
David Woodhouse <dwmw2@infradead.org>,
joro@8bytes.org, the arch/x86 maintainers <x86@kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
iommu@lists.linux-foundation.org, jdmason@kudzu.us,
xen-devel@lists.xenproject.org, robin.murphy@arm.com,
linux-arm-kernel@lists.infradead.org, m.szyprowski@samsung.com
Subject: Re: remove the ->mapping_error method from dma_map_ops V2
Date: Thu, 22 Nov 2018 17:07:15 +0000 [thread overview]
Message-ID: <20181122170715.GI30658@n2100.armlinux.org.uk> (raw)
In-Reply-To: <CAHk-=wh=_T=A53+o4zLNbKio43LGqVDb0KCbWPDvAg54bRDmWw@mail.gmail.com>
On Thu, Nov 22, 2018 at 08:50:47AM -0800, Linus Torvalds wrote:
> On Thu, Nov 22, 2018 at 6:03 AM Christoph Hellwig <hch@lst.de> wrote:
> >
> > 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.
>
> Hmm. Maybe not limit it to just all ones, but actually use the
> (standard, for the kernel) IS_ERR_VALUE()?
>
> That basically reserves the last 4095 values in an unsigned long for
> error values.
>
> Then those functions could actually return *what* error they
> encountered, using just plain
>
> return -ENOMEM;
>
> or whatever?
Linus,
I'm afraid that won't work very well - 32 bit platforms with 64-bit
addresses (LPAE) would have dma_addr_t as a 64-bit value, which
wouldn't fit into an unsigned long.
IS_ERR_VALUE() would cast a 64-bit DMA address down to a 32-bit
pointer (effectively masking with 0xffffffff). It would have the
effect of making (eg) 0xXXXXXXXX_fffffVVV an error, where XXXXXXXX
are any of the top 32-bits of a 64-bit bus address, and VVV is the
error code value.
That could be a problem if you hit it in several places throughout
your available RAM... we'd have to mark every top page of RAM in
a naturally aligned 4GB as unusable, as well as block the top page
in natually aligned 4GB blocks from IOMMUs... and then what about
buses that have weird offsets...
So, I don't think the IS_ERR_VALUE() would work very well.
--
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:[~2018-11-22 17:07 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-22 14:02 remove the ->mapping_error method from dma_map_ops V2 Christoph Hellwig
2018-11-22 14:02 ` [PATCH 01/24] dma-direct: Make DIRECT_MAPPING_ERROR viable for SWIOTLB Christoph Hellwig
2018-11-22 14:02 ` [PATCH 02/24] swiotlb: Skip cache maintenance on map error Christoph Hellwig
2018-11-22 14:02 ` [PATCH 03/24] dma-mapping: provide a generic DMA_MAPPING_ERROR Christoph Hellwig
2018-11-22 14:03 ` [PATCH 04/24] dma-direct: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-22 14:03 ` [PATCH 05/24] arm: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 06/24] powerpc/iommu: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 07/24] mips/jazz: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 08/24] s390: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 09/24] sparc: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 10/24] parisc/ccio: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 11/24] parisc/sba_iommu: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 12/24] arm64: remove the dummy_dma_ops mapping_error method Christoph Hellwig
2018-11-22 14:03 ` [PATCH 13/24] alpha: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-22 14:03 ` [PATCH 14/24] ia64/sba_iommu: improve internal map_page users Christoph Hellwig
2018-11-22 14:03 ` [PATCH 15/24] ia64/sba_iommu: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-22 14:03 ` [PATCH 16/24] ia64/sn: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 17/24] x86/amd_gart: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 18/24] x86/calgary: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 19/24] iommu: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 20/24] iommu/intel: small map_page cleanup Christoph Hellwig
2018-11-22 14:03 ` [PATCH 21/24] iommu/vt-d: remove the mapping_error dma_map_ops method Christoph Hellwig
2018-11-22 14:03 ` [PATCH 22/24] iommu/dma-iommu: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 23/24] xen-swiotlb: " Christoph Hellwig
2018-11-22 14:03 ` [PATCH 24/24] dma-mapping: " Christoph Hellwig
2018-11-22 16:50 ` remove the ->mapping_error method from dma_map_ops V2 Linus Torvalds
2018-11-22 17:07 ` Russell King - ARM Linux [this message]
2018-11-22 17:09 ` Linus Torvalds
2018-11-22 17:14 ` Russell King - ARM Linux
2018-11-22 17:52 ` Robin Murphy
2018-11-22 17:55 ` Linus Torvalds
2018-11-22 18:05 ` Russell King - ARM Linux
2018-11-23 6:57 ` Christoph Hellwig
2018-11-23 6:55 ` Christoph Hellwig
2018-11-28 7:41 ` Christoph Hellwig
2018-11-28 16:47 ` Linus Torvalds
2018-11-28 17:45 ` Russell King - ARM Linux
2018-11-28 18:00 ` Linus Torvalds
2018-11-28 18:08 ` Russell King - ARM Linux
2018-11-28 19:23 ` Russell King - ARM Linux
[not found] ` <CAHk-=whcbiSxSUprsKjVPEdN5-+o8WnTGiKxEV-+HbKNDs=iNA@mail.gmail.com>
2018-11-28 19:31 ` Russell King - ARM Linux
2018-11-29 16:23 ` Christoph Hellwig
2018-11-29 17:44 ` Linus Torvalds
2018-11-29 18:31 ` Christoph Hellwig
2018-11-29 18:53 ` Linus Torvalds
2018-11-29 18:55 ` Christoph Hellwig
2018-11-28 19:27 ` David Miller
2018-11-28 19:47 ` Russell King - ARM Linux
2018-11-28 23:01 ` Shuah Khan
2018-11-23 10:49 ` Joerg Roedel
2018-11-23 11:01 ` Russell King - ARM Linux
2018-11-23 13:03 ` Joerg Roedel
2018-11-23 13:20 ` Russell King - ARM Linux
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