From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: "'Benjamin Herrenschmidt'" <benh@kernel.crashing.org>,
linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org,
"'Arnd Bergmann'" <arnd@arndb.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
Date: Thu, 28 Apr 2011 11:51:31 +0100 [thread overview]
Message-ID: <20110428105131.GD17290@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <003e01cc058f$94beb490$be3c1db0$%szyprowski@samsung.com>
On Thu, Apr 28, 2011 at 12:32:32PM +0200, Marek Szyprowski wrote:
> On Thursday, April 28, 2011 11:38 AM Russell King - ARM Linux wrote:
> > > > > 2. Implement dma_alloc_noncoherent on ARM. Marek pointed out
> > > > > that this is needed, and it currently is not implemented, with
> > > > > an outdated comment explaining why it used to not be possible
> > > > > to do it.
> > > >
> > > > dma_alloc_noncoherent is an entirely pointless API afaics.
> > >
> > > I was about to ask what the point is ... (what is the expected
> > > semantic ? Memory that is reachable but not necessarily cache
> > > coherent ?)
> >
> > As far as I can see, dma_alloc_noncoherent() should just be a wrapper
> > around the normal page allocation function. I don't see it ever needing
> > to do anything special - and the advantage of just being the normal
> > page allocation function is that its properties are well known and
> > architecture independent.
>
> If there is IOMMU chip that supports pages larger than 4KiB then
> dma_alloc_noncoherent() might try to allocate such larger pages what will
> result in faster access to the buffer (lower iommu tlb miss ratio).
> For large buffers even 64KiB 'pages' gives a significant performance
> improvement.
The memory allocated by dma_alloc_noncoherent() (and dma_alloc_coherent())
has to be virtually contiguous, and DMA contiguous. It is assumed by all
drivers that:
virt = dma_alloc_foo(size, &dma);
cpuaddr = virt + offset;
dmaaddr = dma + offset;
results in the CPU and DMA seeing ultimately the same address for cpuaddr
and dmaaddr for 0 <= offset < size.
The standard alloc_pages() also ensures that if you ask for an order-N
page, you'll end up with that allocation being contiguous - so there's
no difference there.
What I'd suggest is that dma_alloc_noncoherent() should be architecture
independent, and should call into whatever iommu support the device has
to setup an approprite iommu mapping. IOW, I don't see any need for
every architecture to provide its own dma_alloc_noncoherent() allocation
function - or indeed every iommu implementation to deal with the
allocation issues either.
WARNING: multiple messages have this Message-ID (diff)
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
Date: Thu, 28 Apr 2011 11:51:31 +0100 [thread overview]
Message-ID: <20110428105131.GD17290@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <003e01cc058f$94beb490$be3c1db0$%szyprowski@samsung.com>
On Thu, Apr 28, 2011 at 12:32:32PM +0200, Marek Szyprowski wrote:
> On Thursday, April 28, 2011 11:38 AM Russell King - ARM Linux wrote:
> > > > > 2. Implement dma_alloc_noncoherent on ARM. Marek pointed out
> > > > > that this is needed, and it currently is not implemented, with
> > > > > an outdated comment explaining why it used to not be possible
> > > > > to do it.
> > > >
> > > > dma_alloc_noncoherent is an entirely pointless API afaics.
> > >
> > > I was about to ask what the point is ... (what is the expected
> > > semantic ? Memory that is reachable but not necessarily cache
> > > coherent ?)
> >
> > As far as I can see, dma_alloc_noncoherent() should just be a wrapper
> > around the normal page allocation function. I don't see it ever needing
> > to do anything special - and the advantage of just being the normal
> > page allocation function is that its properties are well known and
> > architecture independent.
>
> If there is IOMMU chip that supports pages larger than 4KiB then
> dma_alloc_noncoherent() might try to allocate such larger pages what will
> result in faster access to the buffer (lower iommu tlb miss ratio).
> For large buffers even 64KiB 'pages' gives a significant performance
> improvement.
The memory allocated by dma_alloc_noncoherent() (and dma_alloc_coherent())
has to be virtually contiguous, and DMA contiguous. It is assumed by all
drivers that:
virt = dma_alloc_foo(size, &dma);
cpuaddr = virt + offset;
dmaaddr = dma + offset;
results in the CPU and DMA seeing ultimately the same address for cpuaddr
and dmaaddr for 0 <= offset < size.
The standard alloc_pages() also ensures that if you ask for an order-N
page, you'll end up with that allocation being contiguous - so there's
no difference there.
What I'd suggest is that dma_alloc_noncoherent() should be architecture
independent, and should call into whatever iommu support the device has
to setup an approprite iommu mapping. IOW, I don't see any need for
every architecture to provide its own dma_alloc_noncoherent() allocation
function - or indeed every iommu implementation to deal with the
allocation issues either.
next prev parent reply other threads:[~2011-04-28 10:51 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 ` [Linaro-mm-sig] " Alex Deucher
2011-04-27 16:16 ` 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 [this message]
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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