On Tue, Jun 26, 2012 at 08:48:18PM -0600, Stephen Warren wrote:

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On 06/26/2012 08:32 PM, Mark Zhang wrote:

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On 06/26/2012 07:46 PM, Mark Zhang wrote:

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On Tue, 26 Jun 2012 12:55:13 +0200 Thierry Reding
[off-list ref] wrote:

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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:

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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?

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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.

Wasn't the whole point of using a carveout supposed to be a replacement for the
GART? As such I'd think the carveout should rather be a property of the host1x
device.

AIUI what we want to do is have a large contiguous region of memory that a
central component (host1x) manages as a pool from which clients (DRM, V4L, ...)
can allocate buffers as needed. Since all of this memory will be contiguous
anyway there isn't much use for the GART anymore.

I have the same understanding. We don't need GART anymore if carveout is enabled.
I'm thinking that why we need to define a property and reference to global 
/memreserve/ in GART or HOST1X node?
We can just define a label for /memreserve/, so we can distinguish these memory 
reservations already in codes.

But maybe I'm misunderstanding.

Thierry

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