Re: Tegra DRM device tree bindings

[Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>]

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On Tue, Jun 26, 2012 at 08:48:18PM -0600, Stephen Warren wrote:
> 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-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org> 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.

That doesn't work, unfortunately. The /memreserve/ label isn't even
stored in the DTB. Even DTC throws an error when you try to reference
the /memreserve/ by label.

Thierry

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