Re: [PATCH] v4l: async: make v4l2 coexists with devicetree nodes in a dt overlay

Javi Merino
2016-11-23T16:03:13Z

On Wed, Nov 23, 2016 at 11:25:39AM -0300, Javier Martinez Canillas wrote:
> Hello Javi,
>
> On 11/23/2016 07:09 AM, Javi Merino wrote:
> > In asd's configured with V4L2_ASYNC_MATCH_OF, if the v4l2 subdev is in
> > a devicetree overlay, its of_node pointer will be different each time
> > the overlay is applied. We are not interested in matching the
> > pointer, what we want to match is that the path is the one we are
> > expecting. Change to use of_node_cmp() so that we continue matching
> > after the overlay has been removed and reapplied.
> >
>
> I'm still not that familiar with DT overlays (and I guess others aren't
> either) so I think that including an example of a base tree and overlay
> DTS where this is an issue, could make things more clear in the commit.
>
> IIUC, it should be something like this?
>
> -- base tree --
>
> &i2c1 {
> camera: camera@10 {
> reg = <0x10>;
> port {
> cam_ep: endpoint {
> ...
> };
> };
> };
> };
>
> &media_bridge {
> ...
> ports {
> port@0 {
> reg = <0>;
> ep: endpoint {
> remote-endpoint = <&cam_ep>;
> };
> };
> };
> };
>
> -- overlay --
>
> /plugin/;
> / {
> ...
> fragment@0 {
> target = <&camera>;
> __overlay__ {
> compatible = "foo,bar";
> ...
> port {
> cam_ep: endpoint {
> ...
> };
> };
> };
> }
> }

Yes, that's right. What I have is that the whole camera can be
plugged or unplugged, so the overlay adds/removes the camera node:

/ {
fragment@0 {
target-path = "/i2c0";
__overlay__ {
my_cam {
compatible = "foo,bar";
port {
camera0: endpoint {
remote-endpoint = <&vin2a>;
...
};
};
};
};
};

I will add it to the commit message.

> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> > Cc: Javier Martinez Canillas <javier@osg.samsung.com>
> > Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
> > Signed-off-by: Javi Merino <javi.merino@kernel.org>
> > ---
> > Hi,
> >
> > I feel it is a bit of a hack, but I couldn't think of anything better.
> > I'm ccing devicetree@ and Pantelis because there may be a simpler
> > solution.
> >
>
> I also couldn't think a better way to do this, since IIUC the node's name is
> the only thing that doesn't change, and is available at the time the bridge
> driver calls v4l2_async_notifier_register() when parsing the base tree.
>
> > drivers/media/v4l2-core/v4l2-async.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> > index 5bada20..d33a17c 100644
> > --- a/drivers/media/v4l2-core/v4l2-async.c
> > +++ b/drivers/media/v4l2-core/v4l2-async.c
> > @@ -42,7 +42,8 @@ static bool match_devname(struct v4l2_subdev *sd,
> >
> > static bool match_of(struct v4l2_subdev *sd, struct v4l2_async_subdev *asd)
> > {
> > - return sd->of_node == asd->match.of.node;
> > + return !of_node_cmp(of_node_full_name(sd->of_node),
> > + of_node_full_name(asd->match.of.node));
> > }
> >
> > static bool match_custom(struct v4l2_subdev *sd, struct v4l2_async_subdev *asd)
> >
>
> Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
>
> Best regards,
> --
> Javier Martinez Canillas
> Open Source Group
> Samsung Research America