From: Tomasz Figa <tfiga@chromium.org>
To: Christoph Hellwig <hch@lst.de>
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>
Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API
Date: Tue, 8 Dec 2020 13:54:00 +0900 [thread overview]
Message-ID: <CAAFQd5BBEbmENrrZ-vMK9cKOap19XWmfcxwrxKfjWx-wEew8rg@mail.gmail.com> (raw)
In-Reply-To: <20201201144916.GA14682@lst.de>
Hi Christoph,
On Tue, Dec 1, 2020 at 11:49 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Tue, Dec 01, 2020 at 12:36:58PM +0900, Sergey Senozhatsky wrote:
> > Not that I have any sound experience in this area, but the helper
> > probably won't hurt. Do you also plan to add vmap() to that helper
> > or dma_alloc_noncontiguous()/sg_alloc_table_from_pages() only?
>
> Yes, I think adding the vmap is useful, and it probably makes sense
> to do that unconditionally. I'd also include the fallback to
> dma_alloc_pages when the noncontig version isn't supported in the
> helper.
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.
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.
Other than that, again, thanks a lot for helping with this.
Best regards,
Tomasz
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next prev parent reply other threads:[~2020-12-08 4:54 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 [this message]
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
2020-12-10 5:08 ` Tomasz Figa
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