Problem with dma_alloc_coherent at linux-2.6.33-arm1 , withRealView platform,board PBX-A9 and armv7 instructions.

[Catalin Marinas]

On Tue, 2010-07-20 at 04:17 +0100, David Yang wrote:
> On Mon, Jul 19, 2010 at 8:29 PM, Catalin Marinas
> <catalin.marinas at arm.com> wrote:
> > On Sat, 2010-07-17 at 08:05 +0100, David Yang wrote:
> >> I have a question: in linux-2.6.28, there is no barriers in the IO
> >> accessors.
> >
> > Because in 2.6.28 we used Strongly Ordered memory for the coherent DMA
> > buffers and on many CPUs SO accesses are ordered relatively to Device
> > accesses. But that even this isn't guaranteed by the ARM ARM.
> >
> 
> Yes, I know that.
> 
> But I mean that ,in linux-2.6.28,whether the order between the IO
> access will be re-ordered at the hardware level? And whether we should
> use the wmb() to guarantee the order? Here we just talk about the IO
> register access,without the normal memory or coherent DMA buffers.

IO accesses (via Device memory mapping) are guaranteed by the hardware
to be ordered (i.e. they reach the device in the specified program
order).

-- 
Catalin