dma_alloc_coherent fails in framebuffer

[James Bottomley]

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