Re: [PATCH 0/2] Device Tree support for CMA (Contiguous Memory Allocator)

[Olof Johansson <olof-nZhT3qVonbNeoWH0uzbU5w@public.gmane.org>]

On Mon, Feb 18, 2013 at 2:25 PM, Sylwester Nawrocki
<sylvester.nawrocki-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> My context was a multiprocessor SoC, where one of the processors is somehow
> application specific (e.g. camera ISP) and can be considered as a slave
> subsystem, running it's firmware and sharing system memory with the main
> processor.
>
> The slave subsystem can have insane constraints on the memory region where
> its firmware is located and which it also uses as its generic purpose RAM.
>
> While the region assigned to such a slave device would also likely include
> a memory for its DMA buffers, the main concern here was an allocation of
> a working memory for the slave processor.
>
> Perhaps the device tree is not a perfect place for defining exact memory
> regions. If we happen to decide against it, then I guess some set of
> properties would be needed, that would allow CMA to assign appropriate
> memory region(s) to a device.

The place to add such constraints are in the bindings for the camera ISP.

This isn't that different from how dma-window properties used on some
of the PowerPC platforms; it specifies (among other things) the
available address space as seen from the bus/device side.


-Olof