Tegra DRM device tree bindings

[Thierry Reding]

On Wed, Jun 27, 2012 at 03:59:07PM +0300, Hiroshi Doyu wrote:
> On Wed, 27 Jun 2012 07:14:18 +0200
> Thierry Reding <thierry.reding at avionic-design.de> wrote:
> 
> > * PGP Signed by an unknown key
> > 
> > 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 at avionic-design.de> 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.
> > 
> > Wasn't the whole point of using a carveout supposed to be a replacement
> > for the GART?
> 
> Mostly agree. IIUC, we use both carveout/gart allocated buffers in
> android/tegra2.
> 
> >As such I'd think the carveout should rather be a property
> > of the host1x device.
> 
> Rather than introducing a new property, how about using
> "coherent_pool=??M" in the kernel command line if necessary? I think
> that this carveout size depends on the system usage/load.

I was hoping that we could get away with using the CMA and perhaps
initialize it based on device tree content. I agree that the carveout
size depends on the use-case, but I still think it makes sense to
specify it on a per-board basis.

Thierry
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