Re: Tegra DRM device tree bindings

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

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On Tue, Jun 26, 2012 at 11:41:43AM -0600, Stephen Warren wrote:
> On 06/26/2012 08:02 AM, Terje Bergström wrote:
> > On 26.06.2012 16:41, Thierry Reding wrote:
> > 
> >> On Tue, Jun 26, 2012 at 04:01:05PM +0300, Terje Bergström wrote:
> >>> We also assign certain host1x common resources per device by convention,
> >>> f.ex. sync points, channels etc. We currently encode that information in
> >>> the device node (3D uses sync point number X, 2D uses numbers Y and Z).
> >>> The information is not actually describing hardware, as it just
> >>> describes the convention, so I'm not sure if device tree is the proper
> >>> place for it.
> >> Are they configurable? If so I think we should provide for them being
> >> specified in the device tree. They are still hardware resources being
> >> assigned to devices.
> > 
> > Yes, they're configurable, and there's nothing hardware specific in the
> > assignment of a sync point to a particular use. It's all just a software
> > agreement. That's why I'm a bit hesitant on putting it in device trees,
> > which are supposed to only describe hardware.
> 
> So I think that the DT can describe the existence of sync-points
> (presumably include a node for the sync-point HW device if it's
> separate). However, since the usage of each sync-point is entirely
> arbitrary, that seems like something which should be either assigned
> dynamically at run-time, or at least managed/assigned in SW at runtime
> somehow, rather than hard-coded into DT; it's more policy than HW.

The sync-points are part of the host1x device as I understand it. If
their usage is truly generic, then we can probably ignore them safely.
Maybe it'd make sense to carry a property that defines the number of
sync points available for the host1x hardware represented by the DT?

> >>> Either way is fine for me. The full addresses are more familiar to me as
> >>> we tend to use them internally.
> >
> >> Using the OF mechanism for translating the host1x bus addresses,
> >> relative to the host1x base address, to CPU addresses seems "purer", but
> >> either way should work fine.
> > 
> > I'll let you decide, as I don't have a strong opinion either way. I
> > guess whatever is the more common way wins.
> 
> I'd certainly prefer all the nodes to use the full/absolute address.
> That way, the DT will exactly match the addresses in the documentation.

Okay, I'll leave the ranges property as it is now.

Thierry

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