From: Robin Murphy <robin.murphy@arm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Arnd Bergmann <arnd@kernel.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
r.czerwinski@pengutronix.de, linux-media@vger.kernel.org,
devicetree@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
Hector Martin <marcan@marcan.st>,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Rob Herring <robh+dt@kernel.org>,
Alexander Graf <graf@amazon.com>,
Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
Mohamed Mediouni <mohamed.mediouni@caramail.com>,
Mark Kettenis <mark.kettenis@xs4all.nl>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Stan Skowronek <stan@corellium.com>
Subject: Re: [PATCH v4 0/3] Apple M1 DART IOMMU driver
Date: Fri, 16 Jul 2021 16:32:50 +0100 [thread overview]
Message-ID: <0d20bd6b-d0a1-019c-6398-b12f83f4fdf7@arm.com> (raw)
In-Reply-To: <YPEmA0rdXHiGtHSx@infradead.org>
On 2021-07-16 07:24, Christoph Hellwig wrote:
> On Wed, Jul 14, 2021 at 07:19:50PM +0100, Robin Murphy wrote:
>> Even at the DMA API level you could hide *some* of it (at the cost of
>> effectively only having 1/4 of the usable address space), but there are
>> still cases like where v4l2 has a hard requirement that a page-aligned
>> scatterlist can be mapped into a contiguous region of DMA addresses.
>
> Where does v4l2 make that broken assumption? Plenty of dma mapping
> implementations including dma-direct do not support that.
See vb2_dc_get_contiguous_size() and its callers. I still remember
spending an entire work day on writing one email at the culmination of
this discussion:
https://lore.kernel.org/linux-iommu/56409B6D.5090903@arm.com/
809eac54cdd6 was framed as an efficiency improvement because it
technically was one (and something I had wanted to implement anyway),
but it was also very much to save myself from any further email debates
or customer calls about "regressing" code ported from 32-bit platforms...
Robin.
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prev parent reply other threads:[~2021-07-16 15:33 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-27 14:34 [PATCH v4 0/3] Apple M1 DART IOMMU driver Sven Peter via iommu
2021-06-27 14:34 ` [PATCH v4 1/3] iommu: io-pgtable: add DART pagetable format Sven Peter via iommu
2021-06-28 10:54 ` Alexander Graf via iommu
2021-06-29 7:37 ` Sven Peter via iommu
2021-06-29 12:04 ` Alexander Graf via iommu
2021-06-30 13:53 ` Alyssa Rosenzweig
2021-07-13 19:17 ` Robin Murphy
2021-07-14 17:39 ` Sven Peter via iommu
2021-06-27 14:34 ` [PATCH v4 2/3] dt-bindings: iommu: add DART iommu bindings Sven Peter via iommu
2021-06-30 13:54 ` Alyssa Rosenzweig
2021-06-27 14:34 ` [PATCH v4 3/3] iommu: dart: Add DART iommu driver Sven Peter via iommu
2021-06-30 13:49 ` Alyssa Rosenzweig
2021-07-12 11:02 ` Sven Peter via iommu
2021-07-12 13:53 ` Alyssa Rosenzweig
2021-07-13 23:23 ` Robin Murphy
2021-07-15 16:41 ` Sven Peter via iommu
2021-07-19 18:15 ` Robin Murphy
2021-07-25 12:40 ` Sven Peter via iommu
2021-07-26 13:19 ` Alyssa Rosenzweig
2021-07-14 18:19 ` [PATCH v4 0/3] Apple M1 DART IOMMU driver Robin Murphy
2021-07-14 20:51 ` Arnd Bergmann
2021-07-15 6:52 ` Joerg Roedel
2021-07-16 6:24 ` Christoph Hellwig
2021-07-16 15:32 ` Robin Murphy [this message]
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