From: Russell King <rmk@arm.linux.org.uk>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Takashi Iwai <tiwai@suse.de>,
linux-arch@vger.kernel.org,
Gerhard Pircher <gerhard_pircher@gmx.net>,
Parisc List <linux-parisc@vger.kernel.org>
Subject: Re: [PATCH 3/8] parisc: implement dma_mmap_coherent()
Date: Fri, 10 Jul 2009 19:16:20 +0100 [thread overview]
Message-ID: <20090710181620.GA1019@flint.arm.linux.org.uk> (raw)
In-Reply-To: <1247238689.3936.16.camel@mulgrave.site>
On Fri, Jul 10, 2009 at 03:11:29PM +0000, James Bottomley wrote:
> The design of coherent memory was for memory based device mailboxes
> managed by the kernel ... trying to give userspace coherent access to
> the same mailbox is problematic because it gives a direct way for the
> process to interfere with a device function ... shouldn't whatever
> you're trying to do be better accomplished by using an API to control
> the device and keeping the coherent mailbox fully in the kernel address
> space?
As far as sound DMA goes, it's not about mailboxes. It's about a circular
buffer which you want the device to DMA from direct to/from the DAC/ADC
and have the application write/read data directly to/from that same
buffer.
Without this, you end up having to copy the sound data - at something
around 200KB/s from applications into a driver managed buffer, which is
quite an unnecessary overhead for the CPU.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
next prev parent reply other threads:[~2009-07-10 18:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-10 13:10 [PATCH 0/8] Add dma_mmap_coherent() for other archs Takashi Iwai
2009-07-10 13:12 ` [PATCH 1/8] mips: implement dma_mmap_coherent() Takashi Iwai
2009-07-10 13:13 ` [PATCH 2/8] arm: Define ARCH_HAS_DMA_MMAP_COHERENT Takashi Iwai
2009-07-10 13:13 ` [PATCH 3/8] parisc: implement dma_mmap_coherent() Takashi Iwai
2009-07-10 15:11 ` James Bottomley
2009-07-10 18:16 ` Russell King [this message]
2009-07-10 18:30 ` James Bottomley
2009-07-10 18:39 ` Russell King
2009-07-10 18:59 ` James Bottomley
2009-07-17 14:13 ` Takashi Iwai
2009-07-17 19:16 ` James Bottomley
2009-07-19 12:23 ` Takashi Iwai
2009-07-10 13:14 ` [PATCH 4/8] sh: " Takashi Iwai
2009-07-10 13:14 ` [PATCH 5/8] sparc: " Takashi Iwai
2009-07-10 13:15 ` [PATCH 6/8] powerpc: " Takashi Iwai
2009-07-10 13:15 ` [PATCH 7/8] x86: " Takashi Iwai
2009-07-10 13:16 ` [PATCH 8/8] ia64: " Takashi Iwai
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