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

[Ajay kumar <ajaynumb@gmail.com>]

On Fri, Sep 19, 2014 at 7:58 PM, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
> 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.
Agreed.

>> 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?
Oops, my bad!  Panel should also be present in the DT binding(for which,
I am using a phandle for panel node)

>> 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.
Well, I am okay with using video ports to describe the relationship
between the encoder, bridge and the panel.
But, its just that I need to make use of 2 functions when phandle
does it using just one function ;)
-        panel_node = of_parse_phandle(dev->of_node, "panel", 0)
+       endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
+       if (!endpoint)
+               return -EPROBE_DEFER;
+
+       panel_node = of_graph_get_remote_port_parent(endpoint);
+       if (!panel_node)
+               return -EPROBE_DEFER;


If nobody else has objections over using of_graph functions instead
of phandles, I can respin this patchset by making use of video ports.

Ajay

> 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
>
>