From mboxrd@z Thu Jan  1 00:00:00 1970
From: James.Bottomley@HansenPartnership.com (James Bottomley)
Date: Tue, 16 Oct 2012 07:41:41 -0700
Subject: dma_alloc_coherent fails in framebuffer
In-Reply-To: <CAA_GA1cPE+m8N1LQA2iOym4jbFwcHG+K2p-3iBovPWuf1N1q+g@mail.gmail.com>
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To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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