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

On Mon, Feb 18, 2013 at 2:25 PM, Sylwester Nawrocki
[off-list ref] 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