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From: Arnd Bergmann <arnd@arndb.de>
To: Tomasz Figa <tfiga@chromium.org>
Cc: Christoph Hellwig <hch@lst.de>,
	"open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joerg Roedel <joro@8bytes.org>, Will Deacon <will.deacon@arm.com>,
	Vineet Gupta <vgupta@synopsys.com>,
	Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>,
	Mitchel Humpherys <mitchelh@codeaurora.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Sakari Ailus <sakari.ailus@iki.fi>,
	Pawel Osciak <posciak@chromium.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Linux Media Mailing List <linux-media@vger.kernel.org>
Subject: Re: [RFC PATCH 1/5] base: dma-mapping: Export commonly used symbols
Date: Thu, 6 Jul 2017 15:56:26 +0200	[thread overview]
Message-ID: <CAK8P3a2HS4O9fr2iWK6SjuZ7eiUL37y4SegsLGrf=z6DHtUb2w@mail.gmail.com> (raw)
In-Reply-To: <CAAFQd5DS1NxKh4OJ52T2AJNTHg6K2fnuDm5-GHzmUk-kjowf2w@mail.gmail.com>

On Thu, Jul 6, 2017 at 3:31 PM, Tomasz Figa <tfiga@chromium.org> wrote:
> On Thu, Jul 6, 2017 at 9:23 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Thu, Jul 6, 2017 at 10:36 AM, Tomasz Figa <tfiga@chromium.org> wrote:
>>> On Thu, Jul 6, 2017 at 5:34 PM, Tomasz Figa <tfiga@chromium.org> wrote:
>>>
>>> Sorry, I intended to mean:
>>>
>>> IMHO re-implementing the code that's already there in videobuf2 again
>>> in the driver, only because, for no good reason mentioned as for now,
>>> having a loadable module providing DMA ops was disliked, would make no
>>> sense.
>>
>> Why would we need to duplicate that code? I would expect that the videobuf2
>> core can simply call the regular dma_mapping interfaces, and you handle the
>> IOPTE generation at the point when the buffer is handed off from the core
>> code to the device driver. Am I missing something?
>
> Well, for example, the iommu-dma helpers already implement all the
> IOVA management, SG iterations, IOMMU API calls, sanity checks and so
> on. There is a significant amount of common code.
>
> On the other hand, if it's strictly about base/dma-mapping, we might
> not need it indeed. The driver could call iommu-dma helpers directly,
> without the need to provide its own DMA ops.

Yes, that's what I meant: if using the IOMMU interface helps, I don't
see anything wrong with that, but using the iommu based
dma_map_ops seems like it may introduce more problems than
it solves.

        Arnd

WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
To: Tomasz Figa <tfiga-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Cc: Linux Media Mailing List
	<linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Greg Kroah-Hartman
	<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
	Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>,
	"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Krzysztof Kozlowski
	<krzk-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Hans Verkuil <hverkuil-qWit8jRvyhVmR6Xm/wNWPw@public.gmane.org>,
	"open list:IOMMU DRIVERS"
	<iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
	Sakari Ailus <sakari.ailus-X3B1VOXEql0@public.gmane.org>,
	Laurent Pinchart
	<laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>,
	Vineet Gupta <vgupta-HKixBCOQz3hWk0Htik3J/w@public.gmane.org>,
	Hans-Christian Noren Egtvedt
	<egtvedt-BrfabpQBY5qlHtIdYg32fQ@public.gmane.org>,
	Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>,
	Pawel Osciak <posciak-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Subject: Re: [RFC PATCH 1/5] base: dma-mapping: Export commonly used symbols
Date: Thu, 6 Jul 2017 15:56:26 +0200	[thread overview]
Message-ID: <CAK8P3a2HS4O9fr2iWK6SjuZ7eiUL37y4SegsLGrf=z6DHtUb2w@mail.gmail.com> (raw)
In-Reply-To: <CAAFQd5DS1NxKh4OJ52T2AJNTHg6K2fnuDm5-GHzmUk-kjowf2w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

On Thu, Jul 6, 2017 at 3:31 PM, Tomasz Figa <tfiga-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> wrote:
> On Thu, Jul 6, 2017 at 9:23 PM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
>> On Thu, Jul 6, 2017 at 10:36 AM, Tomasz Figa <tfiga-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> wrote:
>>> On Thu, Jul 6, 2017 at 5:34 PM, Tomasz Figa <tfiga-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> wrote:
>>>
>>> Sorry, I intended to mean:
>>>
>>> IMHO re-implementing the code that's already there in videobuf2 again
>>> in the driver, only because, for no good reason mentioned as for now,
>>> having a loadable module providing DMA ops was disliked, would make no
>>> sense.
>>
>> Why would we need to duplicate that code? I would expect that the videobuf2
>> core can simply call the regular dma_mapping interfaces, and you handle the
>> IOPTE generation at the point when the buffer is handed off from the core
>> code to the device driver. Am I missing something?
>
> Well, for example, the iommu-dma helpers already implement all the
> IOVA management, SG iterations, IOMMU API calls, sanity checks and so
> on. There is a significant amount of common code.
>
> On the other hand, if it's strictly about base/dma-mapping, we might
> not need it indeed. The driver could call iommu-dma helpers directly,
> without the need to provide its own DMA ops.

Yes, that's what I meant: if using the IOMMU interface helps, I don't
see anything wrong with that, but using the iommu based
dma_map_ops seems like it may introduce more problems than
it solves.

        Arnd

  parent reply	other threads:[~2017-07-06 13:56 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-05  7:12 [RFC PATCH 0/5] Fixes for loadable modules implementing DMA/IOMMU APIs Tomasz Figa
2017-07-05  7:12 ` [RFC PATCH 1/5] base: dma-mapping: Export commonly used symbols Tomasz Figa
2017-07-05  7:12   ` Tomasz Figa
2017-07-05 15:17   ` Christoph Hellwig
2017-07-05 15:17     ` Christoph Hellwig
2017-07-05 15:22     ` Tomasz Figa
2017-07-05 15:22       ` Tomasz Figa
2017-07-05 17:20       ` Christoph Hellwig
2017-07-05 17:20         ` Christoph Hellwig
2017-07-06  1:44         ` Tomasz Figa
2017-07-06  1:44           ` Tomasz Figa
2017-07-06  8:26           ` Arnd Bergmann
2017-07-06  8:26             ` Arnd Bergmann
2017-07-06  8:34             ` Tomasz Figa
2017-07-06  8:34               ` Tomasz Figa
2017-07-06  8:36               ` Tomasz Figa
2017-07-06 12:23                 ` Arnd Bergmann
2017-07-06 12:23                   ` Arnd Bergmann
2017-07-06 13:31                   ` Tomasz Figa
2017-07-06 13:31                     ` Tomasz Figa
2017-07-06 13:49                     ` Tomasz Figa
2017-07-06 14:02                       ` Arnd Bergmann
2017-07-06 14:02                         ` Arnd Bergmann
2017-07-06 14:06                         ` Tomasz Figa
2017-07-06 14:27                           ` Arnd Bergmann
2017-07-06 14:27                             ` Arnd Bergmann
2017-07-06 14:35                             ` Tomasz Figa
2017-07-06 13:56                     ` Arnd Bergmann [this message]
2017-07-06 13:56                       ` Arnd Bergmann
2017-07-05  7:12 ` [RFC PATCH 2/5] base: dma-mapping: Provide a function to look up remapped pages Tomasz Figa
2017-07-05  7:12   ` Tomasz Figa
2017-07-05  7:12 ` [RFC PATCH 3/5] iommu: Export non-static functions to use in modules Tomasz Figa
2017-07-05  7:12   ` Tomasz Figa
2017-07-05  7:12 ` [RFC PATCH 4/5] iommu/dma: " Tomasz Figa
2017-07-05  7:12   ` Tomasz Figa
2017-07-05 16:22   ` Robin Murphy
2017-07-05 16:22     ` Robin Murphy
2017-07-06  2:25     ` Tomasz Figa
2017-07-06  2:25       ` Tomasz Figa
2017-07-06 11:09       ` Robin Murphy
2017-07-06 11:09         ` Robin Murphy
2017-07-06 14:10         ` Christoph Hellwig
2017-07-06 14:10           ` Christoph Hellwig
2017-07-06 14:17           ` Tomasz Figa
2017-07-06 14:24             ` Tomasz Figa
2017-07-06 14:24               ` Tomasz Figa
2017-07-06 14:35               ` Arnd Bergmann
2017-07-06 14:41                 ` Tomasz Figa
2017-07-05  7:12 ` [RFC PATCH 5/5] iommu/dma: Add iommu_dma_cleanup() Tomasz Figa
2017-07-05  7:12   ` Tomasz Figa

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