From: James.Bottomley@HansenPartnership.com (James Bottomley)
To: linux-arm-kernel@lists.infradead.org
Subject: dma_alloc_coherent fails in framebuffer
Date: Tue, 16 Oct 2012 07:41:41 -0700 [thread overview]
Message-ID: <1350398501.2532.12.camel@dabdike> (raw)
In-Reply-To: <CAA_GA1cPE+m8N1LQA2iOym4jbFwcHG+K2p-3iBovPWuf1N1q+g@mail.gmail.com>
On Tue, 2012-10-16 at 10:17 +0800, Bob Liu wrote:
> I think you need to declare that memory using
> dma_declare_coherent_memory() before
> alloc_from_coherent.
This isn't true. Almost every platform has a mechanism for
manufacturing coherent memory (in the worst case, they just turn off the
CPU cache on a page and hand it out). The purpose of
dma_declare_coherent_memory() is to allow a per device declaration of
preferred regions ... usually because they reside either on the fast
path to the device or sometimes on the device itself. There are only a
handful of devices which need it, so in the ordinary course of events,
dma_alloc_coherent() is used without any memory declaration.
James
WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Bob Liu <lliubbo@gmail.com>
Cc: Tony Prisk <linux@prisktech.co.nz>, Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org,
Arm Kernel Mailing List <linux-arm-kernel@lists.infradead.org>,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: dma_alloc_coherent fails in framebuffer
Date: Tue, 16 Oct 2012 07:41:41 -0700 [thread overview]
Message-ID: <1350398501.2532.12.camel@dabdike> (raw)
In-Reply-To: <CAA_GA1cPE+m8N1LQA2iOym4jbFwcHG+K2p-3iBovPWuf1N1q+g@mail.gmail.com>
On Tue, 2012-10-16 at 10:17 +0800, Bob Liu wrote:
> I think you need to declare that memory using
> dma_declare_coherent_memory() before
> alloc_from_coherent.
This isn't true. Almost every platform has a mechanism for
manufacturing coherent memory (in the worst case, they just turn off the
CPU cache on a page and hand it out). The purpose of
dma_declare_coherent_memory() is to allow a per device declaration of
preferred regions ... usually because they reside either on the fast
path to the device or sometimes on the device itself. There are only a
handful of devices which need it, so in the ordinary course of events,
dma_alloc_coherent() is used without any memory declaration.
James
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next prev parent reply other threads:[~2012-10-16 14:41 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-14 5:28 dma_alloc_coherent fails in framebuffer Tony Prisk
2012-10-14 20:34 ` Tony Prisk
2012-10-14 20:34 ` Tony Prisk
2012-10-14 22:26 ` Tony Prisk
2012-10-14 22:26 ` Tony Prisk
2012-10-15 6:42 ` Tomasz Figa
2012-10-15 6:42 ` Tomasz Figa
2012-10-15 8:03 ` Tony Prisk
2012-10-15 8:03 ` Tony Prisk
2012-10-15 13:35 ` Marek Szyprowski
2012-10-15 13:35 ` Marek Szyprowski
2012-10-15 9:45 ` Mel Gorman
2012-10-15 9:45 ` Mel Gorman
2012-10-15 18:28 ` Tony Prisk
2012-10-15 18:28 ` Tony Prisk
2012-10-16 2:17 ` Bob Liu
2012-10-16 2:17 ` Bob Liu
2012-10-16 5:02 ` Tony Prisk
2012-10-16 5:54 ` Tony Prisk
2012-10-16 5:54 ` Tony Prisk
2012-10-16 6:50 ` Tony Prisk
2012-10-16 6:50 ` Tony Prisk
2012-10-16 7:58 ` Mel Gorman
2012-10-16 7:58 ` Mel Gorman
2012-10-16 8:13 ` Tony Prisk
2012-10-16 8:13 ` Tony Prisk
2012-10-16 14:41 ` James Bottomley [this message]
2012-10-16 14:41 ` James Bottomley
2012-10-17 2:26 ` Bob Liu
2012-10-17 2:26 ` Bob Liu
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