Re: Tegra DRM device tree bindings

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

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On Tue, Jun 26, 2012 at 11:46:42AM -0600, Stephen Warren wrote:
> On 06/26/2012 07:01 AM, Terje Bergström wrote:
> > On 26.06.2012 13:55, Thierry Reding wrote:
> ...
> >> An alternative would be to call of_platform_populate() from the host1x
> 
> [alternative to making the host1x node contain compatible="simple-bus".]
> 
> >> driver. This has the advantage that it could integrate better with the
> >> host1x bus implementation that Terje is working on, but it also needs
> >> additional code to tear down the devices when the host1x driver is
> >> unloaded because a module reload would try to create duplicate devices
> >> otherwise.
> > 
> > Yes, we already have a bus_type for nvhost, and we have nvhost_device
> > and nvhost_driver that device from device and device_driver
> > respectively. They all accommodate some host1x client device common
> > behavior and data that we need to store. We use the bus_type also to
> > match each device and driver together, but the matching is version
> > sensitive. For example, Tegra2 3D needs different driver than Tegra3 3D.
> 
> I'd certainly like to see some upstream discussion re: why exactly we
> have a custom bus type here. What does it do that a regular platform bus
> doesn't do? Are those features something that would be generally useful
> to add to the existing platform bus? Can we instead add hooks into
> platform bus rather than creating a new bus? I recall you saying that
> the nvhost_bus duplicated a lot of code from the existing platform bus.

I don't like the idea of duplicating the code either, but host1x does
have some properties that might be convenient to have part of a bus
abstraction (sync points and channels). This could all be implemented
using a library of functions instead of a bus-type midlayer, though. I
think we've also had that discussion before.

Thierry

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