From: Alex Deucher <alexdeucher@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
Date: Wed, 27 Apr 2011 12:16:49 -0400 [thread overview]
Message-ID: <BANLkTi==KPpTg5PZ61p1xtbBijxND7JUow@mail.gmail.com> (raw)
In-Reply-To: <201104271302.44249.arnd@arndb.de>
On Wed, Apr 27, 2011 at 7:02 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday 27 April 2011, Russell King - ARM Linux wrote:
>> On Wed, Apr 27, 2011 at 10:56:49AM +0200, Arnd Bergmann wrote:
>> > We probably still need to handle both the coherent and noncoherent case
>> > in each dma_map_ops implementation, at least for those combinations where
>> > they matter (definitely the linear mapping). However, I think that using
>> > dma_mapping_common.h would let us use an architecture-independent dma_map_ops
>> > for the generic iommu code that Marek wants to introduce now.
>>
>> The 'do we have an iommu or not' question and the 'do we need to do cache
>> coherency' question are two independent questions which are unrelated to
>> each other. There are four unique but equally valid combinations.
>>
>> Pushing the cache coherency question down into the iommu stuff will mean
>> that we'll constantly be fighting against the 'but this iommu works on x86'
>> shite that we've fought with over block device crap for years. I have
>> no desire to go there.
>
> Ok, I see. I believe we could avoid having to fight with the people that
> only care about coherent architectures if we just have two separate
> implementations of dma_map_ops in the iommu code, one for coherent
> and one for noncoherent DMA. Any architecture that only needs one
> of them would then only enable the Kconfig options for that implementation
> and not care about the other one.
>
>> What we need is a proper abstraction where the DMA ops can say whether
>> they can avoid DMA cache handling (eg, swiotlb or dmabounce stuff) but
>> default to DMA cache handling being the norm - and the DMA cache handling
>> performed in the level above the DMA ops indirection.
>
> Yes, that sounds definitely possible. I guess it could be as simple
> as having a flag somewhere in struct device if we want to make it
> architecture independent.
>
> As for making the default being to do cache handling, I'm not completely
> sure how that would work on architectures where most devices are coherent.
> If I understood the DRM people correctly, some x86 machine have noncoherent
> DMA in their GPUs while everything else is coherent.
On radeon hardware at least the on chip gart mechanism supports both
snooped cache coherent pages and uncached, non-snooped pages.
Alex
>
> Maybe we can default to arch_is_coherent() and allow a device to override
> that when it knows better.
>
> Arnd
>
> _______________________________________________
> Linaro-mm-sig mailing list
> Linaro-mm-sig@lists.linaro.org
> http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
>
WARNING: multiple messages have this Message-ID (diff)
From: alexdeucher@gmail.com (Alex Deucher)
To: linux-arm-kernel@lists.infradead.org
Subject: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
Date: Wed, 27 Apr 2011 12:16:49 -0400 [thread overview]
Message-ID: <BANLkTi==KPpTg5PZ61p1xtbBijxND7JUow@mail.gmail.com> (raw)
In-Reply-To: <201104271302.44249.arnd@arndb.de>
On Wed, Apr 27, 2011 at 7:02 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday 27 April 2011, Russell King - ARM Linux wrote:
>> On Wed, Apr 27, 2011 at 10:56:49AM +0200, Arnd Bergmann wrote:
>> > We probably still need to handle both the coherent and noncoherent case
>> > in each dma_map_ops implementation, at least for those combinations where
>> > they matter (definitely the linear mapping). However, I think that using
>> > dma_mapping_common.h would let us use an architecture-independent dma_map_ops
>> > for the generic iommu code that Marek wants to introduce now.
>>
>> The 'do we have an iommu or not' question and the 'do we need to do cache
>> coherency' question are two independent questions which are unrelated to
>> each other. ?There are four unique but equally valid combinations.
>>
>> Pushing the cache coherency question down into the iommu stuff will mean
>> that we'll constantly be fighting against the 'but this iommu works on x86'
>> shite that we've fought with over block device crap for years. ?I have
>> no desire to go there.
>
> Ok, I see. I believe we could avoid having to fight with the people that
> only care about coherent architectures if we just have two separate
> implementations of dma_map_ops in the iommu code, one for coherent
> and one for noncoherent DMA. Any architecture that only needs one
> of them would then only enable the Kconfig options for that implementation
> and not care about the other one.
>
>> What we need is a proper abstraction where the DMA ops can say whether
>> they can avoid DMA cache handling (eg, swiotlb or dmabounce stuff) but
>> default to DMA cache handling being the norm - and the DMA cache handling
>> performed in the level above the DMA ops indirection.
>
> Yes, that sounds definitely possible. I guess it could be as simple
> as having a flag somewhere in struct device if we want to make it
> architecture independent.
>
> As for making the default being to do cache handling, I'm not completely
> sure how that would work on architectures where most devices are coherent.
> If I understood the DRM people correctly, some x86 machine have noncoherent
> DMA in their GPUs while everything else is coherent.
On radeon hardware at least the on chip gart mechanism supports both
snooped cache coherent pages and uncached, non-snooped pages.
Alex
>
> Maybe we can default to arch_is_coherent() and allow a device to override
> that when it knows better.
>
> ? ? ? ?Arnd
>
> _______________________________________________
> Linaro-mm-sig mailing list
> Linaro-mm-sig at lists.linaro.org
> http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
>
next prev parent reply other threads:[~2011-04-27 16:16 UTC|newest]
Thread overview: 198+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-21 19:29 [RFC] ARM DMA mapping TODO, v1 Arnd Bergmann
2011-04-21 19:29 ` Arnd Bergmann
2011-04-21 20:09 ` [Linaro-mm-sig] " Jesse Barnes
2011-04-21 20:09 ` Jesse Barnes
2011-04-21 21:52 ` Zach Pfeffer
2011-04-21 21:52 ` Zach Pfeffer
2011-04-22 0:34 ` KyongHo Cho
2011-04-22 0:34 ` KyongHo Cho
2011-04-26 14:29 ` Arnd Bergmann
2011-04-26 14:29 ` Arnd Bergmann
2011-04-26 14:28 ` Arnd Bergmann
2011-04-26 14:28 ` Arnd Bergmann
2011-04-26 14:26 ` Arnd Bergmann
2011-04-26 14:26 ` Arnd Bergmann
2011-04-26 15:39 ` Jesse Barnes
2011-04-26 15:39 ` Jesse Barnes
2011-04-27 7:35 ` Russell King - ARM Linux
2011-04-27 7:35 ` Russell King - ARM Linux
2011-04-27 8:56 ` Arnd Bergmann
2011-04-27 8:56 ` Arnd Bergmann
2011-04-27 9:09 ` Russell King - ARM Linux
2011-04-27 9:09 ` Russell King - ARM Linux
2011-04-27 11:02 ` Arnd Bergmann
2011-04-27 11:02 ` Arnd Bergmann
2011-04-27 16:16 ` Alex Deucher [this message]
2011-04-27 16:16 ` [Linaro-mm-sig] " Alex Deucher
2011-04-27 17:44 ` Anca Emanuel
2011-04-27 17:44 ` Anca Emanuel
2011-04-27 20:27 ` Russell King - ARM Linux
2011-04-27 20:27 ` Russell King - ARM Linux
2011-04-27 20:16 ` Russell King - ARM Linux
2011-04-27 20:16 ` Russell King - ARM Linux
2011-04-27 20:21 ` Arnd Bergmann
2011-04-27 20:21 ` Arnd Bergmann
2011-04-27 20:26 ` Russell King - ARM Linux
2011-04-27 20:26 ` Russell King - ARM Linux
2011-04-27 20:48 ` Arnd Bergmann
2011-04-27 20:48 ` Arnd Bergmann
2011-04-27 21:41 ` Benjamin Herrenschmidt
2011-04-27 21:41 ` Benjamin Herrenschmidt
2011-04-28 9:30 ` Russell King - ARM Linux
2011-04-28 9:30 ` Russell King - ARM Linux
2011-04-28 21:07 ` Benjamin Herrenschmidt
2011-04-28 21:07 ` Benjamin Herrenschmidt
2011-04-29 11:26 ` Arnd Bergmann
2011-04-29 11:26 ` Arnd Bergmann
2011-04-29 11:47 ` Benjamin Herrenschmidt
2011-04-29 11:47 ` Benjamin Herrenschmidt
2011-04-29 11:56 ` Alan Cox
2011-04-29 11:56 ` Alan Cox
2011-04-29 22:51 ` Benjamin Herrenschmidt
2011-04-29 22:51 ` Benjamin Herrenschmidt
2011-04-29 12:06 ` [Linaro-mm-sig] " Thomas Hellstrom
2011-04-29 12:06 ` Thomas Hellstrom
2011-04-29 13:34 ` Jerome Glisse
2011-04-29 13:34 ` Jerome Glisse
2011-04-29 22:55 ` Benjamin Herrenschmidt
2011-04-29 22:55 ` Benjamin Herrenschmidt
2011-04-29 22:53 ` Benjamin Herrenschmidt
2011-04-29 22:53 ` Benjamin Herrenschmidt
2011-04-27 10:51 ` Marek Szyprowski
2011-04-27 10:51 ` Marek Szyprowski
2011-04-27 21:37 ` Benjamin Herrenschmidt
2011-04-27 21:37 ` Benjamin Herrenschmidt
2011-04-28 6:40 ` [Linaro-mm-sig] " Arnd Bergmann
2011-04-28 6:40 ` Arnd Bergmann
2011-04-28 6:46 ` FUJITA Tomonori
2011-04-28 6:46 ` FUJITA Tomonori
2011-04-28 9:37 ` Russell King - ARM Linux
2011-04-28 9:37 ` Russell King - ARM Linux
2011-04-28 10:32 ` [Linaro-mm-sig] " Marek Szyprowski
2011-04-28 10:32 ` Marek Szyprowski
2011-04-28 10:51 ` Russell King - ARM Linux
2011-04-28 10:51 ` Russell King - ARM Linux
2011-04-28 12:28 ` Arnd Bergmann
2011-04-28 12:28 ` Arnd Bergmann
2011-04-28 13:15 ` Russell King - ARM Linux
2011-04-28 13:15 ` Russell King - ARM Linux
2011-04-28 14:29 ` Arnd Bergmann
2011-04-28 14:29 ` Arnd Bergmann
2011-04-28 14:34 ` Russell King - ARM Linux
2011-04-28 14:34 ` Russell King - ARM Linux
2011-04-28 14:39 ` Arnd Bergmann
2011-04-28 14:39 ` Arnd Bergmann
2011-04-28 14:58 ` Russell King - ARM Linux
2011-04-28 14:58 ` Russell King - ARM Linux
2011-04-28 19:37 ` Jerome Glisse
2011-04-28 19:37 ` Jerome Glisse
2011-04-29 0:29 ` Benjamin Herrenschmidt
2011-04-29 0:29 ` Benjamin Herrenschmidt
2011-04-29 5:50 ` Thomas Hellstrom
2011-04-29 5:50 ` Thomas Hellstrom
2011-04-29 7:35 ` Benjamin Herrenschmidt
2011-04-29 7:35 ` Benjamin Herrenschmidt
2011-04-29 10:55 ` Thomas Hellstrom
2011-04-29 10:55 ` Thomas Hellstrom
2011-04-29 22:50 ` Benjamin Herrenschmidt
2011-04-29 22:50 ` Benjamin Herrenschmidt
2011-04-29 16:27 ` Jesse Barnes
2011-04-29 16:27 ` Jesse Barnes
2011-04-29 22:46 ` Benjamin Herrenschmidt
2011-04-29 22:46 ` Benjamin Herrenschmidt
2011-04-30 2:45 ` Jesse Barnes
2011-04-30 2:45 ` Jesse Barnes
2011-04-29 7:59 ` Russell King - ARM Linux
2011-04-29 7:59 ` Russell King - ARM Linux
2011-04-29 16:32 ` Jesse Barnes
2011-04-29 16:32 ` Jesse Barnes
2011-04-29 18:29 ` Arnd Bergmann
2011-04-29 18:29 ` Arnd Bergmann
2011-04-29 22:15 ` Russell King - ARM Linux
2011-04-29 22:15 ` Russell King - ARM Linux
2011-05-02 4:42 ` David Brown
2011-05-02 4:42 ` David Brown
2011-05-02 11:26 ` Arnd Bergmann
2011-05-02 11:26 ` Arnd Bergmann
2011-04-29 22:37 ` Benjamin Herrenschmidt
2011-04-29 22:37 ` Benjamin Herrenschmidt
2011-04-29 13:42 ` Joerg Roedel
2011-04-29 13:42 ` Joerg Roedel
2011-04-29 14:19 ` Jerome Glisse
2011-04-29 14:19 ` Jerome Glisse
2011-04-29 15:37 ` Jordan Crouse
2011-04-29 15:37 ` Jordan Crouse
2011-04-28 14:38 ` FUJITA Tomonori
2011-04-28 14:38 ` FUJITA Tomonori
2011-04-29 0:25 ` Benjamin Herrenschmidt
2011-04-29 0:25 ` Benjamin Herrenschmidt
2011-04-29 11:21 ` Arnd Bergmann
2011-04-29 11:21 ` Arnd Bergmann
2011-04-28 10:41 ` Joerg Roedel
2011-04-28 10:41 ` Joerg Roedel
2011-04-28 11:01 ` Russell King - ARM Linux
2011-04-28 11:01 ` Russell King - ARM Linux
2011-04-28 12:25 ` Joerg Roedel
2011-04-28 12:25 ` Joerg Roedel
2011-04-28 12:42 ` Russell King - ARM Linux
2011-04-28 12:42 ` Russell King - ARM Linux
2011-04-28 12:59 ` Joerg Roedel
2011-04-28 12:59 ` Joerg Roedel
2011-04-28 13:02 ` Arnd Bergmann
2011-04-28 13:02 ` Arnd Bergmann
2011-04-28 13:19 ` Russell King - ARM Linux
2011-04-28 13:19 ` Russell King - ARM Linux
2011-04-28 13:56 ` Joerg Roedel
2011-04-28 13:56 ` Joerg Roedel
2011-04-28 14:30 ` Russell King - ARM Linux
2011-04-28 14:30 ` Russell King - ARM Linux
2011-04-27 9:52 ` Catalin Marinas
2011-04-27 9:52 ` Catalin Marinas
2011-04-27 10:43 ` Arnd Bergmann
2011-04-27 10:43 ` Arnd Bergmann
2011-04-27 11:08 ` Catalin Marinas
2011-04-27 11:08 ` Catalin Marinas
2011-04-28 0:15 ` Valdis.Kletnieks
2011-04-28 0:15 ` Valdis.Kletnieks at vt.edu
2011-04-28 8:27 ` Catalin Marinas
2011-04-28 8:27 ` Catalin Marinas
2011-04-28 12:12 ` Arnd Bergmann
2011-04-28 12:12 ` Arnd Bergmann
2011-04-28 12:36 ` Russell King - ARM Linux
2011-04-28 12:36 ` Russell King - ARM Linux
2011-04-28 12:48 ` Arnd Bergmann
2011-04-28 12:48 ` Arnd Bergmann
2011-05-03 14:45 ` Dave Martin
2011-05-03 14:45 ` Dave Martin
2011-04-29 15:41 ` [Linaro-mm-sig] " Arnd Bergmann
2011-04-29 15:41 ` Arnd Bergmann
2011-04-29 16:42 ` Catalin Marinas
2011-04-29 16:42 ` Catalin Marinas
2011-05-03 15:05 ` [Linaro-mm-sig] " Laurent Pinchart
2011-05-03 15:05 ` Laurent Pinchart
2011-05-03 15:31 ` Arnd Bergmann
2011-05-03 15:31 ` Arnd Bergmann
2011-04-27 14:06 ` FUJITA Tomonori
2011-04-27 14:06 ` FUJITA Tomonori
2011-04-27 14:29 ` Catalin Marinas
2011-04-27 14:29 ` Catalin Marinas
2011-04-27 14:34 ` FUJITA Tomonori
2011-04-27 14:34 ` FUJITA Tomonori
2011-04-27 20:29 ` Russell King - ARM Linux
2011-04-27 20:29 ` Russell King - ARM Linux
2011-04-27 21:45 ` Benjamin Herrenschmidt
2011-04-27 21:45 ` Benjamin Herrenschmidt
2011-04-28 7:24 ` [Linaro-mm-sig] " KyongHo Cho
2011-04-28 7:24 ` KyongHo Cho
2011-04-28 8:31 ` Catalin Marinas
2011-04-28 8:31 ` Catalin Marinas
2011-04-27 21:31 ` Benjamin Herrenschmidt
2011-04-27 21:31 ` Benjamin Herrenschmidt
2011-04-28 9:42 ` Russell King - ARM Linux
2011-04-28 9:42 ` Russell King - ARM Linux
2011-04-28 10:27 ` Joerg Roedel
2011-04-28 10:27 ` Joerg Roedel
2011-04-28 12:15 ` Arnd Bergmann
2011-04-28 12:15 ` Arnd Bergmann
2011-05-03 14:35 [Linaro-mm-sig] " Laurent Pinchart
2011-05-03 14:35 ` Laurent Pinchart
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