Date:   Tue, 10 Mar 2020 14:54:37 +0000
From:   Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
To:     Niklas <niklas.soderlund@...natech.se>
CC:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Lad Prabhakar <prabhakar.csengg@...il.com>
Subject: RE: [PATCH v2 1/3] media: rcar-csi2: Add support to match fwnode
 against remote or parent port

Hi Niklas,

Thank you for the review.

> -----Original Message-----
> From: Niklas <niklas.soderlund@...natech.se>
> Sent: 10 March 2020 12:44
> To: Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>; linux-
> media@...r.kernel.org; linux-renesas-soc@...r.kernel.org; linux-
> kernel@...r.kernel.org; Lad Prabhakar <prabhakar.csengg@...il.com>
> Subject: Re: [PATCH v2 1/3] media: rcar-csi2: Add support to match fwnode
> against remote or parent port
>
> Hi Lad,
>
> Thanks for your work.
>
> On 2020-03-10 11:06:02 +0000, Lad Prabhakar wrote:
> > The rcar-csi2 driver uses the v4l2-async framework to do endpoint
> > matching instead of node matching. This is needed as it needs to work
> > with the adv748x driver which register it self in v4l2-async using
> > endpoints instead of nodes. The reason for this is that from a single
> > DT node it creates multiple subdevices, one for each endpoint.
> >
> > But when using subdevs which register itself in v4l2-async using
> > nodes, the rcar-csi2 driver failed to find the matching endpoint
> > because the match.fwnode was pointing to remote endpoint instead of
> > remote parent port.
> >
> > This commit adds support in rcar-csi2 driver to handle both the cases
> > where subdev registers in v4l2-async using endpoints/nodes, by using
> > match_type as V4L2_ASYNC_MATCH_CUSTOM and implementing the
> match()
> > callback to compare the fwnode of either remote/parent.
>
> This is a novel approach to the solution, and I won't object to it out right. But I
> think the proper solution is to move this logic into v4l2-async instead of
> adding a custom match handler in rcar-csi2.
>
> Think of the reveres use-case, a different CSI-2 receiver who wish to use the
> ADV748x would still have this node vs. endpoint issue.
>
Agreed.

> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-
> lad.rj@...renesas.com>
> > ---
> >  drivers/media/platform/rcar-vin/rcar-csi2.c | 41
> > ++++++++++++++++++++++++++---
> >  1 file changed, 38 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c
> > b/drivers/media/platform/rcar-vin/rcar-csi2.c
> > index faa9fb2..39e1639 100644
> > --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> > +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> > @@ -808,6 +808,41 @@ static int rcsi2_parse_v4l2(struct rcar_csi2 *priv,
> >  return 0;
> >  }
> >
> > +static bool rcsi2_asd_match(struct device *dev,
> > +    struct v4l2_async_subdev *async_sd) {
> > +struct rcar_csi2 *priv = (struct rcar_csi2 *)
> > +  async_sd->match.custom.priv;
> > +struct fwnode_handle *endpoint;
> > +struct fwnode_handle *remote;
> > +struct fwnode_handle *parent;
> > +struct device_node *np;
> > +bool matched = false;
> > +
> > +np = of_graph_get_endpoint_by_regs(priv->dev->of_node, 0, 0);
> > +if (!np) {
> > +dev_err(priv->dev, "Not connected to subdevice\n");
> > +return -EINVAL;
>
> You can't return -EINVAL here as it will be interpreted as a match by the caller
> ;-).  You should not even register a device with v4l2-async if it's not
> connected to an endpoint.
>
My bad.

> > +}
> > +
> > +endpoint = of_fwnode_handle(np);
> > +remote = fwnode_graph_get_remote_endpoint(endpoint);
> > +parent = fwnode_graph_get_remote_port_parent(endpoint);
> > +if (parent) {
>
> This is wrong, we will always have a parent and will always take this code
> path. Hence reducing this to the equivalent of node only matching.
> I applied this patch and tried on M3-N with a ADv748x and the wrong
> endpoints of the ADV7482 is routed to the two CSI-2 receivers, breaking it.
>
I did try the media-tree on M3N but it has many issues for booting, could you please
point me to a tree which I can use for testing.

> I added some debug printouts to explain whats going on:
>
>     * First call
>         dev: rcar-csi2 fea80000.csi2
>         endpoint: /soc/csi2@...a0000/ports/port@...ndpoint
>         remote: /soc/i2c@...d8000/video-receiver@...port@...ndpoint
>         parent: /soc/i2c@...d8000/video-receiver@70
>         dev->fwnode: /soc/csi2@...80000
>         dev->of_node: /soc/csi2@...80000
>         match: false
>
>     * Second call
>         dev: adv748x 4-0070
>         endpoint: /soc/csi2@...a0000/ports/port@...ndpoint
>         remote: /soc/i2c@...d8000/video-receiver@...port@...ndpoint
>         parent: /soc/i2c@...d8000/video-receiver@70
>         dev->fwnode: /soc/i2c@...d8000/video-receiver@70
>         dev->of_node: /soc/i2c@...d8000/video-receiver@70
>         match: true
>
>     * Third call
>         dev: adv748x 4-0070
>         endpoint: /soc/csi2@...80000/ports/port@...ndpoint
>         remote: /soc/i2c@...d8000/video-receiver@...port@...ndpoint
>         parent: /soc/i2c@...d8000/video-receiver@70
>         dev->fwnode: /soc/i2c@...d8000/video-receiver@70
>         dev->of_node: /soc/i2c@...d8000/video-receiver@70
>         match: true
>
Thank you for the above.

> Now we have a media graph that is completely probed and video devices
> register in the system but you are not able to stream video as the wrong
> CSI-2 transmitter is described in the graph to be connected to the wrong
> receiver.
>
> This only strengthens my view that this should not be fixed with a custom
> matcher in rcar-csi2 but directly in v4l-async. Please see if you can't address
> the issue in the framework to allow node and endpoint matching to co-
> exists.
>
Ill do some more digging 😊

> > +if (parent == dev->fwnode ||
> > +    parent == &dev->of_node->fwnode)
> > +matched = true;
> > +} else if (remote && !matched) {
>
> No need to check !matched here ;-)
>
Agreed.

Cheers,
--Prabhakar

> > +if (remote == dev->fwnode ||
> > +    remote == &dev->of_node->fwnode)
> > +matched = true;
> > +}
>
>
>
> > +
> > +of_node_put(np);
> > +
> > +return matched;
> > +}
> > +
> >  static int rcsi2_parse_dt(struct rcar_csi2 *priv)  {
> >  struct device_node *ep;
> > @@ -833,9 +868,9 @@ static int rcsi2_parse_dt(struct rcar_csi2 *priv)
> >  return ret;
> >  }
> >
> > -priv->asd.match.fwnode =
> > -
> fwnode_graph_get_remote_endpoint(of_fwnode_handle(ep));
> > -priv->asd.match_type = V4L2_ASYNC_MATCH_FWNODE;
> > +priv->asd.match.custom.match = &rcsi2_asd_match;
> > +priv->asd.match.custom.priv = priv;
> > +priv->asd.match_type = V4L2_ASYNC_MATCH_CUSTOM;
> >
> >  of_node_put(ep);
> >
> > --
> > 2.7.4
> >
>
> --
> Regards,
> Niklas Söderlund


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