From: Mike Frysinger <vapier.adi@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: "Pekka Enberg" <penberg@cs.helsinki.fi>,
"Matt Mackall" <mpm@selenic.com>,
"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Oskar Schirmer" <os@emlix.com>,
"Michael Hennerich" <Michael.Hennerich@analog.com>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
"Daniel Glöckner" <dg@emlix.com>,
"Oliver Schneidewind" <osw@emlix.com>,
"Johannes Weiner" <jw@emlix.com>, "Nick Piggin" <npiggin@suse.de>,
"David Rientjes" <rientjes@google.com>,
"David Brownell" <dbrownell@users.sourceforge.net>,
"Grant Likely" <grant.likely@secretlab.ca>
Subject: Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines
Date: Tue, 11 May 2010 16:54:41 -0400 [thread overview]
Message-ID: <AANLkTimzxrZyQAfocTwIt5zCVyXP7bReKOvP4K7m8epO@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1005111544330.8388@router.home>
On Tue, May 11, 2010 at 16:46, Christoph Lameter wrote:
> On Tue, 11 May 2010, Mike Frysinger wrote:
>> > DMA. If the arch can only DMA into cacheline aligned objects then the
>> > correct method is to force kmalloc alignment to cacheline size.
>>
>> these are SPI drivers and are usable on any arch that supports a SPI
>> bus (which is pretty much every arch). forget about "embedded"
>> arches.
>>
>> the issue here is simple: a SPI driver (AD7877) needs to do a receive
>> SPI transfer into a DMA safe buffer. what is the exact API to
>> dynamically allocate memory for the structure with this buffer
>> embedded in it such that the start of the structure is cached aligned
>> ? creating a dedicated kmem cache may work, but it isnt a scalable
>> solution if every SPI driver needs to create its own cache.
>
> kmalloc returns a pointer to a DMA safe buffer. There is no requirement on
> the x86 hardware that the DMA buffers have to be cache aligned. Cachelines
> will be invalidated as needed.
so this guarantee is made by the kmalloc() API ? and for arches where
the cacheline invalidation is handled in software rather than
hardware, they must declare a min alignment value for kmalloc to be at
least as big as their cache alignment ?
does the phrase "DMA safe buffer" imply cache alignment ?
-mike
WARNING: multiple messages have this Message-ID (diff)
From: Mike Frysinger <vapier.adi@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: "Pekka Enberg" <penberg@cs.helsinki.fi>,
"Matt Mackall" <mpm@selenic.com>,
"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Oskar Schirmer" <os@emlix.com>,
"Michael Hennerich" <Michael.Hennerich@analog.com>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
"Daniel Glöckner" <dg@emlix.com>,
"Oliver Schneidewind" <osw@emlix.com>,
"Johannes Weiner" <jw@emlix.com>, "Nick Piggin" <npiggin@suse.de>,
"David Rientjes" <rientjes@google.com>,
"David Brownell" <dbrownell@users.sourceforge.net>,
"Grant Likely" <grant.likely@secretlab.ca>
Subject: Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines
Date: Tue, 11 May 2010 16:54:41 -0400 [thread overview]
Message-ID: <AANLkTimzxrZyQAfocTwIt5zCVyXP7bReKOvP4K7m8epO@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1005111544330.8388@router.home>
On Tue, May 11, 2010 at 16:46, Christoph Lameter wrote:
> On Tue, 11 May 2010, Mike Frysinger wrote:
>> > DMA. If the arch can only DMA into cacheline aligned objects then the
>> > correct method is to force kmalloc alignment to cacheline size.
>>
>> these are SPI drivers and are usable on any arch that supports a SPI
>> bus (which is pretty much every arch). forget about "embedded"
>> arches.
>>
>> the issue here is simple: a SPI driver (AD7877) needs to do a receive
>> SPI transfer into a DMA safe buffer. what is the exact API to
>> dynamically allocate memory for the structure with this buffer
>> embedded in it such that the start of the structure is cached aligned
>> ? creating a dedicated kmem cache may work, but it isnt a scalable
>> solution if every SPI driver needs to create its own cache.
>
> kmalloc returns a pointer to a DMA safe buffer. There is no requirement on
> the x86 hardware that the DMA buffers have to be cache aligned. Cachelines
> will be invalidated as needed.
so this guarantee is made by the kmalloc() API ? and for arches where
the cacheline invalidation is handled in software rather than
hardware, they must declare a min alignment value for kmalloc to be at
least as big as their cache alignment ?
does the phrase "DMA safe buffer" imply cache alignment ?
-mike
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next prev parent reply other threads:[~2010-05-11 20:55 UTC|newest]
Thread overview: 124+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-06 10:37 [PATCH] ad7877: fix spi word size to 16 bit Oskar Schirmer
2010-05-06 10:37 ` Oskar Schirmer
2010-05-06 10:37 ` [PATCH] ad7877: keep dma rx buffers in seperate cache lines Oskar Schirmer
2010-05-06 18:46 ` Mike Frysinger
2010-05-06 18:46 ` Mike Frysinger
2010-05-07 10:15 ` Oskar Schirmer
2010-05-07 10:15 ` Oskar Schirmer
2010-05-07 18:28 ` Mike Frysinger
2010-05-07 18:28 ` Mike Frysinger
2010-05-08 22:32 ` Johannes Weiner
2010-05-08 22:32 ` Johannes Weiner
2010-05-09 4:45 ` Mike Frysinger
2010-05-09 4:45 ` Mike Frysinger
2010-05-09 8:50 ` Oskar Schirmer
2010-05-09 8:50 ` Oskar Schirmer
2010-05-07 12:07 ` Johannes Weiner
2010-05-10 10:34 ` [PATCH v2] " Oskar Schirmer
2010-05-10 10:34 ` Oskar Schirmer
2010-05-10 10:42 ` [PATCH v3] " Oskar Schirmer
2010-05-10 10:42 ` Oskar Schirmer
2010-05-10 16:39 ` Mike Frysinger
2010-05-10 20:54 ` Dmitry Torokhov
2010-05-10 21:22 ` Andrew Morton
2010-05-10 21:27 ` Mike Frysinger
2010-05-11 6:05 ` Dmitry Torokhov
2010-05-11 6:05 ` Dmitry Torokhov
2010-05-11 6:11 ` Mike Frysinger
2010-05-11 6:11 ` Mike Frysinger
2010-05-11 3:20 ` Andrew Morton
2010-05-11 6:21 ` Dmitry Torokhov
2010-05-11 6:23 ` Mike Frysinger
2010-05-11 6:23 ` Mike Frysinger
2010-05-11 6:33 ` Dmitry Torokhov
2010-05-11 6:33 ` Dmitry Torokhov
2010-05-11 6:37 ` Mike Frysinger
2010-05-11 6:42 ` Pekka Enberg
2010-05-11 13:57 ` Christoph Lameter
2010-05-11 16:52 ` Dmitry Torokhov
2010-05-11 17:31 ` Mike Frysinger
2010-05-11 18:59 ` Pekka Enberg
2010-05-11 20:03 ` Mike Frysinger
2010-05-11 20:07 ` Matt Mackall
2010-05-11 20:10 ` Mike Frysinger
2010-05-11 20:10 ` Mike Frysinger
2010-05-11 20:21 ` Christoph Lameter
2010-05-11 20:34 ` Mike Frysinger
2010-05-11 20:38 ` Pekka Enberg
2010-05-11 20:43 ` Mike Frysinger
2010-05-11 20:43 ` Mike Frysinger
2010-05-11 20:47 ` Pekka Enberg
2010-05-13 6:21 ` Paul Mundt
2010-05-11 20:46 ` Christoph Lameter
2010-05-11 20:54 ` Mike Frysinger [this message]
2010-05-11 20:54 ` Mike Frysinger
2010-05-11 21:01 ` Pekka Enberg
2010-05-11 21:11 ` Mike Frysinger
2010-05-11 21:11 ` Mike Frysinger
2010-05-12 1:58 ` FUJITA Tomonori
[not found] ` <20100511214836.GH1726@emlix.com>
2010-05-11 21:53 ` Dmitry Torokhov
2010-05-11 22:39 ` Mike Frysinger
2010-05-11 22:39 ` Mike Frysinger
2010-05-12 2:07 ` [LKML] " Marc Gauthier
2010-05-12 3:03 ` Nick Piggin
2010-05-12 3:23 ` FUJITA Tomonori
2010-05-12 4:35 ` Mike Frysinger
2010-05-12 4:35 ` Mike Frysinger
2010-05-12 5:28 ` FUJITA Tomonori
2010-05-12 5:28 ` FUJITA Tomonori
2010-05-12 14:37 ` Mike Frysinger
2010-05-12 14:37 ` Mike Frysinger
2010-05-12 18:11 ` Dmitry Torokhov
2010-05-12 18:28 ` Mike Frysinger
2010-05-12 18:28 ` Mike Frysinger
2010-05-12 10:36 ` Johannes Weiner
2010-05-12 12:35 ` Marc Gauthier
2010-05-12 14:36 ` Mike Frysinger
2010-05-12 14:36 ` Mike Frysinger
2010-05-19 12:48 ` David Woodhouse
2010-05-19 13:07 ` Nick Piggin
2010-05-19 13:17 ` David Woodhouse
2010-05-19 13:36 ` Nick Piggin
2010-05-19 13:44 ` Johannes Weiner
2010-05-19 13:52 ` Nick Piggin
2010-05-19 14:38 ` FUJITA Tomonori
2010-05-19 14:58 ` David Woodhouse
2010-05-20 4:42 ` FUJITA Tomonori
2010-05-19 16:37 ` Dmitry Torokhov
2010-05-19 15:00 ` Johannes Weiner
2010-05-17 6:12 ` Michal Simek
2010-05-19 13:00 ` David Woodhouse
2010-05-11 22:37 ` Alan Cox
2010-05-11 20:22 ` Pekka Enberg
2010-05-11 14:12 ` Oskar Schirmer
2010-05-11 14:12 ` Oskar Schirmer
2010-05-06 11:18 ` [PATCH] ad7877: fix spi word size to 16 bit Hennerich, Michael
2010-05-06 11:18 ` Hennerich, Michael
2010-05-06 18:26 ` Mike Frysinger
2010-05-06 18:26 ` Mike Frysinger
2010-05-07 9:41 ` Daniel Glöckner
2010-05-07 9:41 ` Daniel Glöckner
2010-05-07 18:23 ` Mike Frysinger
2010-05-07 18:23 ` Mike Frysinger
2010-05-13 7:53 ` Dmitry Torokhov
2010-05-13 7:53 ` Dmitry Torokhov
2010-05-15 18:15 ` Oskar Schirmer
2010-05-15 18:15 ` Oskar Schirmer
2010-05-16 19:25 ` Mike Frysinger
2010-05-16 19:25 ` Mike Frysinger
2010-05-17 7:29 ` Oskar Schirmer
2010-05-17 7:29 ` Oskar Schirmer
2010-05-17 8:14 ` Hennerich, Michael
2010-05-17 8:14 ` Hennerich, Michael
2010-05-17 8:41 ` Oskar Schirmer
2010-05-17 8:41 ` Oskar Schirmer
2010-05-17 23:49 ` Mike Frysinger
2010-05-17 23:49 ` Mike Frysinger
2010-05-18 0:18 ` H Hartley Sweeten
2010-05-18 0:18 ` H Hartley Sweeten
2010-05-18 8:32 ` Oskar Schirmer
2010-05-18 8:32 ` Oskar Schirmer
2010-05-18 9:37 ` Daniel Glöckner
2010-05-18 9:37 ` Daniel Glöckner
2010-05-18 8:34 ` [PATCH v2] " Oskar Schirmer
2010-05-18 8:34 ` Oskar Schirmer
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