Re: [PATCH v3 1/2] media: i2c: ov772x: Add support for BT656 mode

Jacopo Mondi
2020-09-04T09:17:11Z

Hi Sakari,

On Fri, Sep 04, 2020 at 11:21:04AM +0300, Sakari Ailus wrote:
> Hi Laurent, Jacopo,
>
> On Fri, Sep 04, 2020 at 09:55:53AM +0200, Jacopo Mondi wrote:
> > Hi Laurent,
> >
> > On Fri, Sep 04, 2020 at 04:20:00AM +0300, Laurent Pinchart wrote:
> > > Hi Prabhakar,
> > >
> > > Thank you for the patch.
> > >
> > > On Mon, Aug 24, 2020 at 08:04:05PM +0100, Lad Prabhakar wrote:
> > > > Add support to read the bus-type and enable BT656 mode if needed.
> > > >
> > > > Also fail probe if unsupported bus_type is detected.
> > > >
> > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > > > Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > > ---
> > > > drivers/media/i2c/ov772x.c | 32 ++++++++++++++++++++++++++++++++
> > > > 1 file changed, 32 insertions(+)
> > > >
> > > > diff --git a/drivers/media/i2c/ov772x.c b/drivers/media/i2c/ov772x.c
> > > > index 2cc6a678069a..67764d647526 100644
> > > > --- a/drivers/media/i2c/ov772x.c
> > > > +++ b/drivers/media/i2c/ov772x.c
> > > > @@ -31,6 +31,7 @@
> > > > #include <media/v4l2-ctrls.h>
> > > > #include <media/v4l2-device.h>
> > > > #include <media/v4l2-event.h>
> > > > +#include <media/v4l2-fwnode.h>
> > > > #include <media/v4l2-image-sizes.h>
> > > > #include <media/v4l2-subdev.h>
> > > >
> > > > @@ -434,6 +435,7 @@ struct ov772x_priv {
> > > > #ifdef CONFIG_MEDIA_CONTROLLER
> > > > struct media_pad pad;
> > > > #endif
> > > > + struct v4l2_fwnode_endpoint ep;
> > > > };
> > > >
> > > > /*
> > > > @@ -581,6 +583,13 @@ static int ov772x_s_stream(struct v4l2_subdev *sd, int enable)
> > > > if (priv->streaming == enable)
> > > > goto done;
> > > >
> > > > + if (priv->ep.bus_type == V4L2_MBUS_BT656) {
> > > > + ret = regmap_update_bits(priv->regmap, COM7, ITU656_ON_OFF,
> > > > + enable ? ITU656_ON_OFF : ~ITU656_ON_OFF);
> > > > + if (ret)
> > > > + goto done;
> > > > + }
> > > > +
> > > > ret = regmap_update_bits(priv->regmap, COM2, SOFT_SLEEP_MODE,
> > > > enable ? 0 : SOFT_SLEEP_MODE);
> > > > if (ret)
> > > > @@ -1354,6 +1363,7 @@ static const struct v4l2_subdev_ops ov772x_subdev_ops = {
> > > >
> > > > static int ov772x_probe(struct i2c_client *client)
> > > > {
> > > > + struct fwnode_handle *endpoint;
> > > > struct ov772x_priv *priv;
> > > > int ret;
> > > > static const struct regmap_config ov772x_regmap_config = {
> > > > @@ -1415,6 +1425,28 @@ static int ov772x_probe(struct i2c_client *client)
> > > > goto error_clk_put;
> > > > }
> > > >
> > > > + endpoint = fwnode_graph_get_next_endpoint(dev_fwnode(&client->dev),
> > > > + NULL);
> > > > + if (!endpoint) {
> > > > + dev_err(&client->dev, "endpoint node not found\n");
> > > > + ret = -EINVAL;
> > > > + goto error_clk_put;
> > > > + }
> > > > +
> > > > + ret = v4l2_fwnode_endpoint_parse(endpoint, &priv->ep);
> > >
> > > v4l2_fwnode_endpoint_parse() is deprecated for new drivers,
> > > v4l2_fwnode_endpoint_alloc_parse() is recommended instead. Please note
> > > that v4l2_fwnode_endpoint_free() then needs to be called in the error
> > > path and in remove().
> >
> > Doesn't alloc_parse() differ from just _parse() as it reserve space
> > for the 'link-frequencies' array ? As this device does not support
> > CSI-2 and the 'link-frequencies' property is not allows in bindings,
> > isn't using endpoint_parse() better as it saves a call to _free() ?
>
> Yeah. I think the documentation needs to be updated.
>
> The thinking was there would be other variable size properties that drivers
> would need but that didn't happen. So feel free to continue use
> v4l2_fwnode_endpoint_parse() where it does the job.
>
> >
> > Or are we deprecating that function unconditionally ? The
> > documentation suggests "please use v4l2_fwnode_endpoint_alloc_parse()
> > in new drivers" but here it doesn't seem required..
> >
> > >
> > > On the other hand, not setting .bus_type and letting the parse()
> > > function determine the but type automatically is also deprecated, and I
> > > don't think forcing drivers to call v4l2_fwnode_endpoint_alloc_parse()
> > > once for each bus type until one succeeds is a good API. As change will
> > > be needed in that API, you can ignore v4l2_fwnode_endpoint_alloc_parse()
> > > for the time being if you want.
> >
> > But indeed relying on auto-guessing of the bus type is deprecated since
> > some time now (and the API could be improved, yes). Sorry I missed
> > that yesterday.
>
> There's one case where the bus type does not need to be set: when bindings
> require it *and* at the same time you have no default configuration that
> requires something to be set in the bus specific struct. Bindings where
> bus-type is required were added later so I think the documentation should
> be changed there, too.
>
> I can send the patches.
>
> >
> > As we support parallel and bt.656 only I must be honest I don't mind
> > it here as otherwise the code would be more complex for no real gain,
> > but I defer this to Sakari which has been fighting the battle against
> > auto-guessing since a long time now :)
>
> I think you should require bus-type property in bindings in that case.
>
> But as it's an existing driver, bus-type will be optional. You'll need to
> default to what was supported earlier. This is actually an interesting case
> as bindings do not document it.

For reference:
https://patchwork.linuxtv.org/project/linux-media/patch/20200903131029.18334-3-jacopo+renesas@jmondi.org/

But yes, we might have DTBs in the wild without bus-type specified :(

>
> >
> >
> > >
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > >
> > > > + fwnode_handle_put(endpoint);
> > > > + if (ret) {
> > > > + dev_err(&client->dev, "Could not parse endpoint\n");
> > > > + goto error_clk_put;
> > > > + }
> > > > +
> > > > + if (priv->ep.bus_type != V4L2_MBUS_PARALLEL &&
> > > > + priv->ep.bus_type != V4L2_MBUS_BT656) {
> > > > + dev_err(&client->dev, "Unsupported bus type %d\n",
> > > > + priv->ep.bus_type);
> > > > + goto error_clk_put;
> > > > + }
> > > > +
> > > > ret = ov772x_video_probe(priv);
> > > > if (ret < 0)
> > > > goto error_gpio_put;
> > >
> > > --
> > > Regards,
> > >
> > > Laurent Pinchart
>
> --
> Sakari Ailus