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From: Christoph Hellwig <hch@lst.de>
To: Tomasz Figa <tfiga@chromium.org>
Cc: Christoph Hellwig <hch@lst.de>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Ricardo Ribalda <ribalda@chromium.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	Sergey Senozhatsky <senozhatsky@google.com>
Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API
Date: Wed, 9 Dec 2020 12:12:35 +0100	[thread overview]
Message-ID: <20201209111235.GA22806@lst.de> (raw)
In-Reply-To: <CAAFQd5BBEbmENrrZ-vMK9cKOap19XWmfcxwrxKfjWx-wEew8rg@mail.gmail.com>

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.

> 
> In any case, Sergey is going to share a preliminary patch on how the
> current API would be used in the V4L2 videobuf2 framework. That should
> give us more input on how such a helper could look.

Awesome!

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: 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>,
	Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API
Date: Wed, 9 Dec 2020 12:12:35 +0100	[thread overview]
Message-ID: <20201209111235.GA22806@lst.de> (raw)
In-Reply-To: <CAAFQd5BBEbmENrrZ-vMK9cKOap19XWmfcxwrxKfjWx-wEew8rg@mail.gmail.com>

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.

> 
> In any case, Sergey is going to share a preliminary patch on how the
> current API would be used in the V4L2 videobuf2 framework. That should
> give us more input on how such a helper could look.

Awesome!
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  parent reply	other threads:[~2020-12-09 11:13 UTC|newest]

Thread overview: 45+ 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
2020-11-25 22:19 ` Ricardo Ribalda
2020-11-26 11:44 ` Sergey Senozhatsky
2020-11-26 11:44   ` Sergey Senozhatsky
2020-11-30  8:31   ` Christoph Hellwig
2020-11-30  8:31     ` Christoph Hellwig
2020-11-30  8:34 ` Christoph Hellwig
2020-11-30  8:34   ` Christoph Hellwig
2020-11-30 10:49   ` Ricardo Ribalda
2020-11-30 10:49     ` Ricardo Ribalda
2020-12-01  3:36   ` Sergey Senozhatsky
2020-12-01  3:36     ` Sergey Senozhatsky
2020-12-01 14:49     ` Christoph Hellwig
2020-12-01 14:49       ` Christoph Hellwig
2020-12-08  4:54       ` Tomasz Figa
2020-12-08  4:54         ` Tomasz Figa
2020-12-08  6:45         ` Sergey Senozhatsky via iommu
2020-12-08  7:13         ` Sergey Senozhatsky
2020-12-08  7:13           ` Sergey Senozhatsky
2020-12-09 11:16           ` . Christoph Hellwig
2020-12-09 11:16             ` . Christoph Hellwig
2021-01-07 14:14             ` Ricardo Ribalda
2021-01-07 14:14               ` Ricardo Ribalda
2021-01-11  8:36               ` . Christoph Hellwig
2021-01-11  8:36                 ` . Christoph Hellwig
2021-01-15 13:08                 ` Ricardo Ribalda
2021-01-15 13:08                   ` Ricardo Ribalda
2021-01-20 17:17                   ` . Christoph Hellwig
2021-01-20 17:17                     ` . Christoph Hellwig
2021-01-26 17:06                   ` . Christoph Hellwig
2021-01-26 17:06                     ` . Christoph Hellwig
2021-01-26 23:29                     ` Ricardo Ribalda
2021-01-26 23:29                       ` Ricardo Ribalda
2021-01-27 15:56                       ` . Christoph Hellwig
2021-01-27 15:56                         ` . Christoph Hellwig
2021-01-27 21:35                         ` Ricardo Ribalda
2021-01-27 21:35                           ` Ricardo Ribalda
2021-01-28  7:57                           ` . Christoph Hellwig
2021-01-28  7:57                             ` . Christoph Hellwig
2020-12-09 11:12         ` Christoph Hellwig [this message]
2020-12-09 11:12           ` Christoph Hellwig
2020-12-09 13:05           ` Robin Murphy
2020-12-09 13:05             ` Robin Murphy
2020-12-10  5:08             ` Tomasz Figa
2020-12-10  5:08               ` Tomasz Figa

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