Re: Tegra DRM device tree bindings

[Stephen Warren <swarren@xxxxxxxxxx>]

On 06/26/2012 08:32 PM, Mark Zhang wrote:
>> On 06/26/2012 07:46 PM, Mark Zhang wrote:
>>>>> On Tue, 26 Jun 2012 12:55:13 +0200
>>>>> Thierry Reding <thierry.reding@xxxxxxxxxxxxxxxxx> wrote:
>> ...
>>>> I'm not sure I understand how information about the carveout would be
>>>> obtained from the IOMMU API, though.
>>>
>>> I think that can be similar with current gart implementation. Define carveout as:
>>>
>>> carveout {
>>>         compatible = "nvidia,tegra20-carveout";
>>>         size = <0x10000000>;
>>> };
>>>
>>> Then create a file such like "tegra-carveout.c" to get these definitions and
>> register itself as platform device's iommu instance.
>>
>> The carveout isn't a HW object, so it doesn't seem appropriate to define a DT
>> node to represent it.
> 
> Yes. But I think it's better to export the size of carveout as a configurable item.
> So we need to define this somewhere. How about define carveout as a property of gart?

There already exists a way of preventing Linux from using certain chunks
of memory; the /memreserve/ syntax. From a brief look at the dtc source,
it looks like /memreserve/ entries can have labels, which implies that a
property in the GART node could refer to the /memreserve/ entry by
phandle in order to know what memory regions to use.
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