From: Robin Murphy <robin.murphy@arm.com>
To: Christoph Hellwig <hch@lst.de>, Tomasz Figa <tfiga@chromium.org>
Cc: Sergey Senozhatsky <senozhatsky@google.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Ricardo Ribalda <ribalda@chromium.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>
Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API
Date: Wed, 9 Dec 2020 13:05:11 +0000 [thread overview]
Message-ID: <6b34596d-34c4-bd99-c5a7-5a4742c5b886@arm.com> (raw)
In-Reply-To: <20201209111235.GA22806@lst.de>
On 2020-12-09 11:12, Christoph Hellwig wrote:
> On Tue, Dec 08, 2020 at 01:54:00PM +0900, Tomasz Figa wrote:
>> >From the media perspective, it would be good to have the vmap
>> optional, similarly to the DMA_ATTR_NO_KERNEL_MAPPING attribute for
>> coherent allocations. Actually, in the media drivers, the need to have
>> a kernel mapping of the DMA buffers corresponds to a minority of the
>> drivers. Most of them only need to map them to the userspace.
>>
>> Nevertheless, that minority actually happens to be quite widely used,
>> e.g. the uvcvideo driver, so we can't go to the other extreme and just
>> drop the vmap at all.
>
> My main problem is that the DMA_ATTR_NO_KERNEL_MAPPING makes a mess
> of an API. I'd much rather have low-level API that returns the
> discontiguous allocations and another one that vmaps them rather
> than starting to overload arguments like in dma_alloc_attrs with
> DMA_ATTR_NO_KERNEL_MAPPING.
Agreed - if iommu-dma's dma_alloc_coherent() ends up as little more than
a thin wrapper around those two functions I think that would be a good
sign. It also seems like it might be a good idea for this API to use
scatterlists rather than page arrays as it's fundamental format, to help
reduce impedance with dma-buf - if we can end up with a wider redesign
that also gets rid of dma_get_sgtable(), all the better!
Robin.
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next prev parent reply other threads:[~2020-12-09 13:05 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-25 22:19 [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API Ricardo Ribalda
2020-11-26 11:44 ` Sergey Senozhatsky
2020-11-30 8:31 ` Christoph Hellwig
2020-11-30 8:34 ` Christoph Hellwig
2020-11-30 10:49 ` Ricardo Ribalda
2020-12-01 3:36 ` Sergey Senozhatsky
2020-12-01 14:49 ` Christoph Hellwig
2020-12-08 4:54 ` Tomasz Figa
2020-12-08 6:45 ` Sergey Senozhatsky via iommu
2020-12-08 7:13 ` Sergey Senozhatsky
2020-12-09 11:16 ` . Christoph Hellwig
2021-01-07 14:14 ` Ricardo Ribalda
2021-01-11 8:36 ` . Christoph Hellwig
2021-01-15 13:08 ` Ricardo Ribalda
2021-01-20 17:17 ` . Christoph Hellwig
2021-01-26 17:06 ` . Christoph Hellwig
2021-01-26 23:29 ` Ricardo Ribalda
2021-01-27 15:56 ` . Christoph Hellwig
2021-01-27 21:35 ` Ricardo Ribalda
2021-01-28 7:57 ` . Christoph Hellwig
2020-12-09 11:12 ` Christoph Hellwig
2020-12-09 13:05 ` Robin Murphy [this message]
2020-12-10 5:08 ` Tomasz Figa
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