Re: Tegra DRM device tree bindings

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 06/27/2012 06:44 AM, Hiroshi Doyu wrote:
...
> I think that there are 2 cases:
> 
>   (1) discontiguous memory with IOMMU
>   (2) contiguous memory without IOMMU(called "carveout" in general?)
...
> For (2), although memory is mostly anonymous one, we may need to know
> how much to allocate, where we only need "size". This size is not from
> h/w feature, but it depends on the system load/usage. So I think that
> this size can be passed from kernel command line? For exmaple, we can
> specify how much contiguous memory is necessary with putting
> "coherent_pool=??M" in the kernel command line as below:
> 
> 	coherent_pool=nn[KMG]	[ARM,KNL]
> 			Sets the size of memory pool for coherent, atomic dma
> 			allocations.

I guess if that's the standard way of initializing CMA, then that's fine.

It'd be nice if there was a way to specify that from the DT too; that
way the user/distro/bootloader constructing the kernel command-line
wouldn't have to remember to add "random" (potentially
Tegra-/board-specific) extra arguments onto the command-line; the Tegra
command-line in the upstream kernel is quite clean right now, especially
compare to the enormous number of options we require downstream:-(