Re: [PATCH V7 11/12] Documentation: bridge: Add documentation for ps8622 DT properties

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 19/09/14 16:59, Ajay kumar wrote:

> I am not really able to understand, what's stopping us from using this
> bridge on a board with "complex" display connections. To use ps8622 driver,
> one needs to "attach" it to the DRM framework. For this, the DRM driver

Remember that when we talk about DT bindings, there's no such thing as
DRM. We talk about hardware. The same bindings need to work on any
operating system.

> would need the DT node for ps8622 bridge. For which I use a phandle.

A complex one could be for example a case where you have two different
panels connected to ps8622, and you can switch between the two panels
with, say, a gpio. How do you present that with a simple phandle?

In the exynos5420-peach-pit.dts, which you linked earlier, I see a
"panel" property in the ps8625 node. That's missing from the bindings in
this patch. Why is that? How is the panel linked in this version?

> If some XYZ platform wishes to pick the DT node via a different method,
> they are always welcome to do it. Just because I am not specifying a
> video port/endpoint in the DT binding example, would it mean that platform
> cannot make use of ports in future? If that is the case, I can add something

All the platforms share the same bindings for ps8622. If you now specify
that ps8622 bindings use a simple phandle, then anyone who uses ps8622
should support that.

Of course the bindings can be extended in the future. In that case the
drivers need to support both the old and the new bindings, which is
always a hassle.

Generally speaking, I sense that we have different views of how display
devices and drivers are structured. You say "If some XYZ platform wishes
to pick the DT node via a different method, they are always welcome to
do it.". This sounds to me that you see the connections between display
devices as something handled by a platform specific driver.

I, on the other hand, see connections between display devices as common
properties.

Say, we could have a display board, with a panel and an encoder and
maybe some other components, which takes parallel RGB as input. The same
display board could as well be connected to an OMAP board or to an
Exynos board.

I think the exact same display-board.dtsi file, which describes the
devices and connections in the display board, should be usable on both
OMAP and Exynos platforms. This means we need to have a common way to
describe video devices, just as we have for other things.

 Tomi



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