Re: [PATCH v6 17/39] platform: add video-multiplexer subdevice driver

[Philipp Zabel]

Hi Sakari,

thank you for the review.

On Tue, 2017-04-04 at 15:47 +0300, Sakari Ailus wrote:
> Hi Steve, Philipp and Pavel,
> 
> On Mon, Mar 27, 2017 at 05:40:34PM -0700, Steve Longerbeam wrote:
> > From: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
> > 
> > This driver can handle SoC internal and external video bus multiplexers,
> > controlled either by register bit fields or by a GPIO. The subdevice
> > passes through frame interval and mbus configuration of the active input
> > to the output side.
> 
> The MUX framework is already in linux-next. Could you use that instead of
> adding new driver + bindings that are not compliant with the MUX framework?
> I don't think it'd be much of a change in terms of code, using the MUX
> framework appears quite simple.

It is not quite clear to me how to design the DT bindings for this. Just
splitting the video-multiplexer driver from the mux-mmio / mux-gpio
would make it necessary to keep the video-multiplexer node to describe
the of-graph bindings. But then we have two different nodes in the DT
that describe the same hardware:

	mux: mux {
		compatible = "mux-gpio";
		mux-gpios = <&gpio 0>, <&gpio 1>;
		#mux-control-cells = <0>;
	}

	video-multiplexer {
		compatible = "video-multiplexer"
		mux-controls = <&mux>;

		ports {
			/* ... */
		}
	}

It would feel more natural to have the ports in the mux node, but then
how would the video-multiplexer driver be instanciated, and how would it
get to the of-graph nodes?

> In general the driver looks pretty good, especially regarding the user space
> API implementation which is important for use with other drivers.
> 
> I have some more detailed comments below.
> 
> > 
> > Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> > Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
> > 
> > - fixed a cut&paste error in vidsw_remove(): v4l2_async_register_subdev()
> >   should be unregister.
> > 
> > - added media_entity_cleanup() to vidsw_remove().
> > 
> > - added missing MODULE_DEVICE_TABLE().
> >   Suggested-by: Javier Martinez Canillas <javier@xxxxxxxxxxxx>
> > 
> > - there was a line left over from a previous iteration that negated
> >   the new way of determining the pad count just before it which
> >   has been removed (num_pads = of_get_child_count(np)).
> > 
> > - removed [gs]_frame_interval ops. timeperframe is not used anywhwere
> >   in this subdev, and currently it has no control over frame rate.
> > 
> > - add link_validate to media_entity_operations.
> > 
> > - moved devicetree binding doc to a separate commit.
> > 
> > - Philipp Zabel has developed a set of patches that allow adding
> >   to the subdev async notifier waiting list using a chaining method
> >   from the async registered callbacks (v4l2_of_subdev_registered()
> >   and the prep patches for that). For now, I've removed the use of
> >   v4l2_of_subdev_registered() for the vidmux driver's registered
> >   callback. This doesn't affect the functionality of this driver,
> >   but allows for it to be merged now, before adding the chaining
> >   support.
> > 
> > Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
> > ---
> >  drivers/media/platform/Kconfig             |   8 +
> >  drivers/media/platform/Makefile            |   2 +
> >  drivers/media/platform/video-multiplexer.c | 451 +++++++++++++++++++++++++++++
> >  3 files changed, 461 insertions(+)
> >  create mode 100644 drivers/media/platform/video-multiplexer.c
> > 
> > diff --git a/drivers/media/platform/Kconfig b/drivers/media/platform/Kconfig
> > index ab0bb48..c9b8d9c 100644
> > --- a/drivers/media/platform/Kconfig
> > +++ b/drivers/media/platform/Kconfig
> > @@ -74,6 +74,14 @@ config VIDEO_M32R_AR_M64278
> >  	  To compile this driver as a module, choose M here: the
> >  	  module will be called arv.
> >  
> > +config VIDEO_MULTIPLEXER
> > +	tristate "Video Multiplexer"
> > +	depends on VIDEO_V4L2_SUBDEV_API && MEDIA_CONTROLLER
> > +	help
> > +	  This driver provides support for SoC internal N:1 video bus
> > +	  multiplexers controlled by register bitfields as well as external
> > +	  2:1 video multiplexers controlled by a single GPIO.
> > +
> >  config VIDEO_OMAP3
> >  	tristate "OMAP 3 Camera support"
> >  	depends on VIDEO_V4L2 && I2C && VIDEO_V4L2_SUBDEV_API && ARCH_OMAP3
> > diff --git a/drivers/media/platform/Makefile b/drivers/media/platform/Makefile
> > index 8959f6e..d418add 100644
> > --- a/drivers/media/platform/Makefile
> > +++ b/drivers/media/platform/Makefile
> > @@ -27,6 +27,8 @@ obj-$(CONFIG_VIDEO_SH_VEU)		+= sh_veu.o
> >  
> >  obj-$(CONFIG_VIDEO_MEM2MEM_DEINTERLACE)	+= m2m-deinterlace.o
> >  
> > +obj-$(CONFIG_VIDEO_MULTIPLEXER)		+= video-multiplexer.o
> > +
> >  obj-$(CONFIG_VIDEO_S3C_CAMIF) 		+= s3c-camif/
> >  obj-$(CONFIG_VIDEO_SAMSUNG_EXYNOS4_IS) 	+= exynos4-is/
> >  obj-$(CONFIG_VIDEO_SAMSUNG_S5P_JPEG)	+= s5p-jpeg/
> > diff --git a/drivers/media/platform/video-multiplexer.c b/drivers/media/platform/video-multiplexer.c
> > new file mode 100644
> > index 0000000..b18c317
> > --- /dev/null
> > +++ b/drivers/media/platform/video-multiplexer.c
> > @@ -0,0 +1,451 @@
> > +/*
> > + * video stream multiplexer controlled via gpio or syscon
> > + *
> > + * Copyright (C) 2013 Pengutronix, Sascha Hauer <kernel@xxxxxxxxxxxxxx>
> > + * Copyright (C) 2016 Pengutronix, Philipp Zabel <kernel@xxxxxxxxxxxxxx>
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; either version 2
> > + * of the License, or (at your option) any later version.
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <linux/err.h>
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/mfd/syscon.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/of_graph.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/regmap.h>
> > +#include <media/v4l2-async.h>
> > +#include <media/v4l2-device.h>
> > +#include <media/v4l2-subdev.h>
> > +#include <media/v4l2-of.h>
> > +
> > +struct vidsw {
> > +	struct v4l2_subdev subdev;
> > +	unsigned int num_pads;
> 
> You could use subdev.entity.num_pads instead of caching the value locally.

Ok, I'll change this.

> > +	struct media_pad *pads;
> > +	struct v4l2_mbus_framefmt *format_mbus;
> > +	struct v4l2_of_endpoint *endpoint;
> > +	struct regmap_field *field;
> > +	struct gpio_desc *gpio;
> > +	int active;
> > +};
> > +
> > +static inline struct vidsw *v4l2_subdev_to_vidsw(struct v4l2_subdev *sd)
> > +{
> > +	return container_of(sd, struct vidsw, subdev);
> > +}
> > +
> > +static void vidsw_set_active(struct vidsw *vidsw, int active)
> > +{
> > +	vidsw->active = active;
> > +	if (active < 0)
> > +		return;
> > +
> > +	dev_dbg(vidsw->subdev.dev, "setting %d active\n", active);
> > +
> > +	if (vidsw->field)
> > +		regmap_field_write(vidsw->field, active);
> > +	else if (vidsw->gpio)
> > +		gpiod_set_value(vidsw->gpio, active);
> > +}
> > +
> > +static int vidsw_link_setup(struct media_entity *entity,
> > +			    const struct media_pad *local,
> > +			    const struct media_pad *remote, u32 flags)
> > +{
> > +	struct v4l2_subdev *sd = media_entity_to_v4l2_subdev(entity);
> > +	struct vidsw *vidsw = v4l2_subdev_to_vidsw(sd);
> > +
> > +	/* We have no limitations on enabling or disabling our output link */
> > +	if (local->index == vidsw->num_pads - 1)
> > +		return 0;
> > +
> > +	dev_dbg(sd->dev, "link setup %s -> %s", remote->entity->name,
> > +		local->entity->name);
> > +
> > +	if (!(flags & MEDIA_LNK_FL_ENABLED)) {
> > +		if (local->index == vidsw->active) {
> > +			dev_dbg(sd->dev, "going inactive\n");
> > +			vidsw->active = -1;
> > +		}
> > +		return 0;
> > +	}
> > +
> > +	if (vidsw->active >= 0) {
> > +		struct media_pad *pad;
> > +
> > +		if (vidsw->active == local->index)
> > +			return 0;
> > +
> > +		pad = media_entity_remote_pad(&vidsw->pads[vidsw->active]);
> > +		if (pad) {
> > +			struct media_link *link;
> > +			int ret;
> > +
> > +			link = media_entity_find_link(pad,
> > +						&vidsw->pads[vidsw->active]);
> > +			if (link) {
> > +				ret = __media_entity_setup_link(link, 0);
> 
> I wouldn't implicitly disable a link, even if only one can be active at a
> given time. No other drivers do that either.
> 
> Perhaps returning an error might be a better thing to do: if you're
> reconfiguring the pipeline anyway, there are likely issues elsewhere in it.
> 
> We could also change the behaviour later to allow implicit changes but we
> can't later on go the other way without breaking the user space.

Fair enough, I'll drop this.

> > +				if (ret)
> > +					return ret;
> > +			}
> > +		}
> > +	}
> > +
> > +	vidsw_set_active(vidsw, local->index);
> > +
> > +	return 0;
> > +}
> > +
> > +static struct media_entity_operations vidsw_ops = {
> > +	.link_setup = vidsw_link_setup,
> > +	.link_validate = v4l2_subdev_link_validate,
> > +};
> > +
> > +static bool vidsw_endpoint_disabled(struct device_node *ep)
> > +{
> > +	struct device_node *rpp;
> > +
> > +	if (!of_device_is_available(ep))
> 
> ep here is the endpoint, whereas the argument to of_device_is_available()
> should correspond to the actual device.

Well, this was a convenience to allow adding status = "disabled" to
endpoints to turn them off (see the function name). I

> > +		return true;
> > +
> > +	rpp = of_graph_get_remote_port_parent(ep);
> > +	if (!rpp)
> > +		return true;
> > +
> > +	return !of_device_is_available(rpp);
> > +}
> > +
> > +static int vidsw_async_init(struct vidsw *vidsw, struct device_node *node)
> 
> I think I'd arrange this closer to probe as it's related to probe directly.
> Up to you.

I'll change this to
	rpp = of_graph_get_remote_port_parent(ep);
	return !of_device_is_available(rpp);
as Steve suggested.

> > +{
> > +	struct device_node *ep;
> > +	u32 portno;
> > +	int numports;
> > +	int ret;
> > +	int i;
> > +	bool active_link = false;
> > +
> > +	numports = vidsw->num_pads;
> > +
> > +	for (i = 0; i < numports - 1; i++)
> > +		vidsw->pads[i].flags = MEDIA_PAD_FL_SINK;
> > +	vidsw->pads[numports - 1].flags = MEDIA_PAD_FL_SOURCE;
> > +
> > +	vidsw->subdev.entity.function = MEDIA_ENT_F_VID_MUX;
> > +	ret = media_entity_pads_init(&vidsw->subdev.entity, numports,
> > +				     vidsw->pads);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	vidsw->subdev.entity.ops = &vidsw_ops;
> > +
> > +	for_each_endpoint_of_node(node, ep) {
> > +		struct v4l2_of_endpoint endpoint;
> > +
> > +		v4l2_of_parse_endpoint(ep, &endpoint);
> > +
> > +		portno = endpoint.base.port;
> > +		if (portno >= numports - 1)
> > +			continue;
> > +
> > +		if (vidsw_endpoint_disabled(ep)) {
> > +			dev_dbg(vidsw->subdev.dev,
> > +				"port %d disabled\n", portno);
> > +			continue;
> > +		}
> > +
> > +		vidsw->endpoint[portno] = endpoint;
> > +
> > +		if (portno == vidsw->active)
> > +			active_link = true;
> > +	}
> > +
> > +	for (portno = 0; portno < numports - 1; portno++) {
> > +		if (!vidsw->endpoint[portno].base.local_node)
> > +			continue;
> > +
> > +		/* If the active input is not connected, use another */
> > +		if (!active_link) {
> > +			vidsw_set_active(vidsw, portno);
> > +			active_link = true;
> > +		}
> > +	}
> > +
> > +	return v4l2_async_register_subdev(&vidsw->subdev);
> > +}
> > +
> > +int vidsw_g_mbus_config(struct v4l2_subdev *sd, struct v4l2_mbus_config *cfg)
> 
> We should get rid of g_mbus_config() in the long run, but as we don't have
> the alternative (frame descriptors) isn't up to the job yet I guess it's ok.
> I don't think we'll have too many users for the video switch right now.

Ok, we can add a comment to mark this as undesirable.

> > +{
> > +	struct vidsw *vidsw = v4l2_subdev_to_vidsw(sd);
> > +	struct media_pad *pad;
> > +	int ret;
> > +
> > +	if (vidsw->active == -1) {
> > +		dev_err(sd->dev, "no configuration for inactive mux\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	/*
> > +	 * Retrieve media bus configuration from the entity connected to the
> > +	 * active input
> > +	 */
> > +	pad = media_entity_remote_pad(&vidsw->pads[vidsw->active]);
> > +	if (pad) {
> > +		sd = media_entity_to_v4l2_subdev(pad->entity);
> > +		ret = v4l2_subdev_call(sd, video, g_mbus_config, cfg);
> > +		if (ret == -ENOIOCTLCMD)
> > +			pad = NULL;
> > +		else if (ret < 0) {
> > +			dev_err(sd->dev, "failed to get source configuration\n");
> > +			return ret;
> > +		}
> > +	}
> > +	if (!pad) {
> > +		/* Mirror the input side on the output side */
> > +		cfg->type = vidsw->endpoint[vidsw->active].bus_type;
> > +		if (cfg->type == V4L2_MBUS_PARALLEL ||
> > +		    cfg->type == V4L2_MBUS_BT656)
> > +			cfg->flags = vidsw->endpoint[vidsw->active].bus.parallel.flags;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int vidsw_s_stream(struct v4l2_subdev *sd, int enable)
> > +{
> > +	struct vidsw *vidsw = v4l2_subdev_to_vidsw(sd);
> > +	struct v4l2_subdev *upstream_sd;
> > +	struct media_pad *pad;
> > +
> > +	if (vidsw->active == -1) {
> > +		dev_err(sd->dev, "Can not start streaming on inactive mux\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	pad = media_entity_remote_pad(&sd->entity.pads[vidsw->active]);
> > +	if (!pad) {
> > +		dev_err(sd->dev, "Failed to find remote source pad\n");
> > +		return -ENOLINK;
> > +	}
> > +
> > +	if (!is_media_entity_v4l2_subdev(pad->entity)) {
> > +		dev_err(sd->dev, "Upstream entity is not a v4l2 subdev\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	upstream_sd = media_entity_to_v4l2_subdev(pad->entity);
> > +
> > +	return v4l2_subdev_call(upstream_sd, video, s_stream, enable);
> 
> Now that we'll have more than two drivers involved in the same pipeline it
> becomes necessary to define the behaviour of s_stream() throughout the
> pipeline --- i.e. whose responsibility is it to call s_stream() on the
> sub-devices in the pipeline?
> 
> I can submit a patch for that. I think the way you do it here is good, as it
> enables the caller to choose the appropriate behaviour, i.e. start the local
> device before or after the upstream sub-device.

Please do, this should be decided before any more complex inter-driver
pipelines show up.

> > +}
> > +
> > +static const struct v4l2_subdev_video_ops vidsw_subdev_video_ops = {
> > +	.g_mbus_config = vidsw_g_mbus_config,
> > +	.s_stream = vidsw_s_stream,
> > +};
> > +
> > +static struct v4l2_mbus_framefmt *
> > +__vidsw_get_pad_format(struct v4l2_subdev *sd,
> > +		       struct v4l2_subdev_pad_config *cfg,
> > +		       unsigned int pad, u32 which)
> > +{
> > +	struct vidsw *vidsw = v4l2_subdev_to_vidsw(sd);
> > +
> > +	switch (which) {
> > +	case V4L2_SUBDEV_FORMAT_TRY:
> > +		return v4l2_subdev_get_try_format(sd, cfg, pad);
> > +	case V4L2_SUBDEV_FORMAT_ACTIVE:
> > +		return &vidsw->format_mbus[pad];
> > +	default:
> > +		return NULL;
> > +	}
> > +}
> > +
> > +static int vidsw_get_format(struct v4l2_subdev *sd,
> > +			    struct v4l2_subdev_pad_config *cfg,
> > +			    struct v4l2_subdev_format *sdformat)
> > +{
> > +	sdformat->format = *__vidsw_get_pad_format(sd, cfg, sdformat->pad,
> > +						   sdformat->which);
> > +	return 0;
> > +}
> > +
> > +static int vidsw_set_format(struct v4l2_subdev *sd,
> > +			    struct v4l2_subdev_pad_config *cfg,
> > +			    struct v4l2_subdev_format *sdformat)
> > +{
> > +	struct vidsw *vidsw = v4l2_subdev_to_vidsw(sd);
> > +	struct v4l2_mbus_framefmt *mbusformat;
> > +
> > +	if (sdformat->pad >= vidsw->num_pads)
> > +		return -EINVAL;
> 
> This check is already performed in v4l2-subdev.c.

Excellent.

> > +
> > +	mbusformat = __vidsw_get_pad_format(sd, cfg, sdformat->pad,
> > +					    sdformat->which);
> > +	if (!mbusformat)
> > +		return -EINVAL;
> > +
> > +	/* Output pad mirrors active input pad, no limitations on input pads */
> 
> Source and sink pads.

Ok.

> > +	if (sdformat->pad == (vidsw->num_pads - 1) && vidsw->active >= 0)
> 
> I think it'd be cleaner to test for the pad flag instead of the number. Or,
> add a macro to obtain the source pad number.
> 
> > +		sdformat->format = vidsw->format_mbus[vidsw->active];
> > +
> > +	*mbusformat = sdformat->format;
> > +
> > +	return 0;
> > +}
> > +
> > +static struct v4l2_subdev_pad_ops vidsw_pad_ops = {
> > +	.get_fmt = vidsw_get_format,
> > +	.set_fmt = vidsw_set_format,
> > +};
> > +
> > +static struct v4l2_subdev_ops vidsw_subdev_ops = {
> > +	.pad = &vidsw_pad_ops,
> > +	.video = &vidsw_subdev_video_ops,
> > +};
> > +
> > +static int of_get_reg_field(struct device_node *node, struct reg_field *field)
> > +{
> > +	u32 bit_mask;
> > +	int ret;
> > +
> > +	ret = of_property_read_u32(node, "reg", &field->reg);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = of_property_read_u32(node, "bit-mask", &bit_mask);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = of_property_read_u32(node, "bit-shift", &field->lsb);
> > +	if (ret < 0)
> > +		return ret;
> 
> I think the above would look nice in a MUX driver. :-)

I'll submit an MMIO / syscon / regmap bitfield mux driver.

> > +
> > +	field->msb = field->lsb + fls(bit_mask) - 1;
> > +
> > +	return 0;
> > +}
> > +
> > +static int vidsw_probe(struct platform_device *pdev)
> > +{
> > +	struct device_node *np = pdev->dev.of_node;
> > +	struct of_endpoint endpoint;
> > +	struct device_node *ep;
> > +	struct reg_field field;
> > +	struct vidsw *vidsw;
> > +	struct regmap *map;
> > +	unsigned int num_pads;
> > +	int ret;
> > +
> > +	vidsw = devm_kzalloc(&pdev->dev, sizeof(*vidsw), GFP_KERNEL);
> > +	if (!vidsw)
> > +		return -ENOMEM;
> > +
> > +	platform_set_drvdata(pdev, vidsw);
> > +
> > +	v4l2_subdev_init(&vidsw->subdev, &vidsw_subdev_ops);
> > +	snprintf(vidsw->subdev.name, sizeof(vidsw->subdev.name), "%s",
> > +			np->name);
> > +	vidsw->subdev.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> > +	vidsw->subdev.dev = &pdev->dev;
> > +
> > +	/*
> > +	 * The largest numbered port is the output port. It determines
> > +	 * total number of pads
> > +	 */
> > +	num_pads = 0;
> 
> You can initialise num_pads in variable declaration.
> 
> > +	for_each_endpoint_of_node(np, ep) {
> > +		of_graph_parse_endpoint(ep, &endpoint);
> > +		num_pads = max(num_pads, endpoint.port + 1);
> 
> Port numbers come directly from DT.
> 
> Shouldn't num_pads be only the number of pads that have links with actual
> physical connections? I.e. if a device is disabled, it shouldn't be
> counted here.

If we only create media pads for the connected DT ports with available
remote device, there is no 1:1 correspondence between pad number and the
physical mux setting anymore, complicating the driver.

> > +	}
> > +
> > +	if (num_pads < 2) {
> > +		dev_err(&pdev->dev, "Not enough ports %d\n", num_pads);
> > +		return -EINVAL;
> > +	}
> > +
> > +	ret = of_get_reg_field(np, &field);
> > +	if (ret == 0) {
> > +		map = syscon_node_to_regmap(np->parent);
> > +		if (!map) {
> > +			dev_err(&pdev->dev, "Failed to get syscon register map\n");
> > +			return PTR_ERR(map);
> > +		}
> > +
> > +		vidsw->field = devm_regmap_field_alloc(&pdev->dev, map, field);
> > +		if (IS_ERR(vidsw->field)) {
> > +			dev_err(&pdev->dev, "Failed to allocate regmap field\n");
> > +			return PTR_ERR(vidsw->field);
> > +		}
> > +
> > +		regmap_field_read(vidsw->field, &vidsw->active);
> > +	} else {
> > +		if (num_pads > 3) {
> > +			dev_err(&pdev->dev, "Too many ports %d\n", num_pads);
> > +			return -EINVAL;
> > +		}
> > +
> > +		vidsw->gpio = devm_gpiod_get(&pdev->dev, NULL, GPIOD_OUT_LOW);
> > +		if (IS_ERR(vidsw->gpio)) {
> > +			dev_warn(&pdev->dev,
> > +				 "could not request control gpio: %d\n", ret);
> > +			vidsw->gpio = NULL;
> > +		}
> > +
> > +		vidsw->active = gpiod_get_value(vidsw->gpio) ? 1 : 0;
> > +	}
> > +
> > +	vidsw->num_pads = num_pads;
> > +	vidsw->pads = devm_kzalloc(&pdev->dev, sizeof(*vidsw->pads) * num_pads,
> > +			GFP_KERNEL);
> > +	vidsw->format_mbus = devm_kzalloc(&pdev->dev,
> > +			sizeof(*vidsw->format_mbus) * num_pads, GFP_KERNEL);
> > +	vidsw->endpoint = devm_kzalloc(&pdev->dev,
> > +			sizeof(*vidsw->endpoint) * (num_pads - 1), GFP_KERNEL);
> > +
> > +	ret = vidsw_async_init(vidsw, np);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return 0;
> > +}
> > +
> > +static int vidsw_remove(struct platform_device *pdev)
> > +{
> > +	struct vidsw *vidsw = platform_get_drvdata(pdev);
> > +	struct v4l2_subdev *sd = &vidsw->subdev;
> > +
> > +	v4l2_async_unregister_subdev(sd);
> > +	media_entity_cleanup(&sd->entity);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id vidsw_dt_ids[] = {
> > +	{ .compatible = "video-multiplexer", },
> > +	{ /* sentinel */ }
> > +};
> > +MODULE_DEVICE_TABLE(of, vidsw_dt_ids);
> > +
> > +static struct platform_driver vidsw_driver = {
> > +	.probe		= vidsw_probe,
> > +	.remove		= vidsw_remove,
> > +	.driver		= {
> > +		.of_match_table = vidsw_dt_ids,
> > +		.name = "video-multiplexer",
> > +	},
> > +};
> > +
> > +module_platform_driver(vidsw_driver);
> > +
> > +MODULE_DESCRIPTION("video stream multiplexer");
> > +MODULE_AUTHOR("Sascha Hauer, Pengutronix");
> > +MODULE_AUTHOR("Philipp Zabel, Pengutronix");
> > +MODULE_LICENSE("GPL");

regards
Philipp