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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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      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 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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