[PATCH 1/2] of: Add helper to lookup non port child node

[Jagan Teki]

On Wed, Dec 8, 2021 at 2:20 AM Rob Herring <robh+dt at kernel.org> wrote:
>
> On Mon, Dec 6, 2021 at 11:49 PM Jagan Teki <jagan at amarulasolutions.com> wrote:
> >
> > Add of_get_non_port_child() helper that can be used to lookup
> > non port child nodes.
> >
> > Some OF graphs don't require 'ports' to represent the next output
> > instead, it simply adds a child node on a given parent node. This
> > helper lookup that child node, however that child node is not a
> > 'port' on given parent as 'port' based nodes are looked up via
> > of_graph_get_remote_node().
> >
> > Example OF graph representation of DSI host, which doesn't
> > have 'ports'.
>
> This seems pretty specific to DSI and also can't handle there being
> more than 1 non-port node. That's allowed for DSI too, but I don't
> think I've ever seen a case. Anyways, I'd just move this to DRM rather
> than common DT code. One comment on the implementation that will
> shrink it.

I think it can be possible to OF graph even for non-DSI, however if
the end-node outputs to a panel or bridge. At the moment, I can one
use case on the non-DSI side is rcar du encoder.
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/rcar-du/rcar_du_encoder.c#n68

I'm not sure this can be done existing of_graph_get_remote_node, but an example.

>
> >
> > dsi {
> >         #address-cells = <1>;
> >         #size-cells = <0>;
> >
> >         port {
> >                 dsi_in_tcon0: endpoint {
> >                         remote-endpoint = <tcon0_out_dsi>;
> >         };
> >
> >         panel at 0 {
> >                 reg = <0>;
> >         };
> > };
> >
> > Signed-off-by: Jagan Teki <jagan at amarulasolutions.com>
> > ---
> >  drivers/of/base.c  | 29 +++++++++++++++++++++++++++++
> >  include/linux/of.h |  6 ++++++
> >  2 files changed, 35 insertions(+)
> >
> > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > index 61de453b885c..31bbf885b0f8 100644
> > --- a/drivers/of/base.c
> > +++ b/drivers/of/base.c
> > @@ -854,6 +854,35 @@ struct device_node *of_get_compatible_child(const struct device_node *parent,
> >  }
> >  EXPORT_SYMBOL(of_get_compatible_child);
> >
> > +/**
> > + * of_get_non_port_child - Find the non port child node for a given parent
> > + * @node:      parent node
> > + *
> > + * This function looks for child node which is not port child for given parent.
> > + *
> > + * Return: A node pointer if found, with refcount incremented, use
> > + * of_node_put() on it when done.
> > + * Returns NULL if node is not found.
> > + */
> > +struct device_node *of_get_non_port_child(const struct device_node *parent)
> > +{
> > +       struct device_node *child;
> > +
> > +       for_each_child_of_node(parent, child) {
>
> for_each_available_child_of_node

Look like this simplifies not required to use of_device_is_available,
I will use it in v2.

Thanks,
Jagan.