Re: [Lkcamp][PATCH] media: vimc: Add vimc-streamer for stream control

[Helen Koike]

Hi Lucas,

Thank you for your patch, just some small comments below.

On 12/15/18 2:46 PM, Lucas A. M. MagalhÃes wrote:
> The previous code pipeline used the stack to walk on the graph and
> process a frame. Basically the vimc-sensor entity starts a thread that
> generates the frames and calls the propagate_process function to send
> this frame to each entity linked with a sink pad. The propagate_process
> will call the process_frame of the entities which will call the
> propagate_frame for each one of it's sink pad. This cycle will continue
> until it reaches a vimc-capture entity that will finally return and
> unstack.
> 
> This solution had many problems:
>   * It was a little bit slow
>   * It was susceptible to a stack overflow as it made indiscriminate
>     use of the stack.
>   * It doesn't allow frame rate control
>   * It was complex to understand
>   * It doesn't allow pipeline control
> 
> This commit proposes an alternative way to control vimc streams by
> having a streamer object. This object will create a linear pipeline
> walking backwards on the graph. When the stream starts it will simply
> loop through the pipeline calling the respective process_frame function
> for each entity on the pipeline.
> 
> This solution has some premises which are true for now:
>   * Two paths can never be enabled and streaming at the same time.
>   * There is no entity streaming frames to two source pads at the same
>     time.
>   * There is no entity receiving frames from two sink pads at the same
>     time.
> 
> Signed-off-by: Lucas A. M. MagalhÃes <lucmaga@xxxxxxxxx>

I won't comment on the commit message, as Mauro already sent a good review.

> ---
> Hi,
> 
> This patch introduces a streamer controller library for the vimc
> driver. It's a step towards a optimized mode I've been discussing with
> Helen.
> I plan to pass a tpg struct through the pipeline. This tpg struct
> will be configured in each entity and the capture will generate the
> frames with the correct format at the end of the pipeline.
> 
> Thanks,
> Lucas
> 
>  drivers/media/platform/vimc/Makefile        |   3 +-
>  drivers/media/platform/vimc/vimc-capture.c  |  18 +-
>  drivers/media/platform/vimc/vimc-common.c   |  50 ++----
>  drivers/media/platform/vimc/vimc-common.h   |  15 +-
>  drivers/media/platform/vimc/vimc-debayer.c  |  26 +--
>  drivers/media/platform/vimc/vimc-scaler.c   |  28 +---
>  drivers/media/platform/vimc/vimc-sensor.c   |  56 ++-----
>  drivers/media/platform/vimc/vimc-streamer.c | 176 ++++++++++++++++++++
>  drivers/media/platform/vimc/vimc-streamer.h |  38 +++++
>  9 files changed, 268 insertions(+), 142 deletions(-)
>  create mode 100644 drivers/media/platform/vimc/vimc-streamer.c
>  create mode 100644 drivers/media/platform/vimc/vimc-streamer.h
> 
> diff --git a/drivers/media/platform/vimc/Makefile b/drivers/media/platform/vimc/Makefile
> index 4b2e3de7856e..c4fc8e7d365a 100644
> --- a/drivers/media/platform/vimc/Makefile
> +++ b/drivers/media/platform/vimc/Makefile
> @@ -5,6 +5,7 @@ vimc_common-objs := vimc-common.o
>  vimc_debayer-objs := vimc-debayer.o
>  vimc_scaler-objs := vimc-scaler.o
>  vimc_sensor-objs := vimc-sensor.o
> +vimc_streamer-objs := vimc-streamer.o
>  
>  obj-$(CONFIG_VIDEO_VIMC) += vimc.o vimc_capture.o vimc_common.o vimc-debayer.o \
> -				vimc_scaler.o vimc_sensor.o
> +			    vimc_scaler.o vimc_sensor.o vimc_streamer.o
> diff --git a/drivers/media/platform/vimc/vimc-capture.c b/drivers/media/platform/vimc/vimc-capture.c
> index 3f7e9ed56633..80d7515ec420 100644
> --- a/drivers/media/platform/vimc/vimc-capture.c
> +++ b/drivers/media/platform/vimc/vimc-capture.c
> @@ -24,6 +24,7 @@
>  #include <media/videobuf2-vmalloc.h>
>  
>  #include "vimc-common.h"
> +#include "vimc-streamer.h"
>  
>  #define VIMC_CAP_DRV_NAME "vimc-capture"
>  
> @@ -44,7 +45,7 @@ struct vimc_cap_device {
>  	spinlock_t qlock;
>  	struct mutex lock;
>  	u32 sequence;
> -	struct media_pipeline pipe;
> +	struct vimc_stream stream;
>  };
>  
>  static const struct v4l2_pix_format fmt_default = {
> @@ -248,14 +249,13 @@ static int vimc_cap_start_streaming(struct vb2_queue *vq, unsigned int count)
>  	vcap->sequence = 0;
>  
>  	/* Start the media pipeline */
> -	ret = media_pipeline_start(entity, &vcap->pipe);
> +	ret = media_pipeline_start(entity, &vcap->stream.pipe);
>  	if (ret) {
>  		vimc_cap_return_all_buffers(vcap, VB2_BUF_STATE_QUEUED);
>  		return ret;
>  	}
>  
> -	/* Enable streaming from the pipe */
> -	ret = vimc_pipeline_s_stream(&vcap->vdev.entity, 1);
> +	ret = vimc_streamer_s_stream(&vcap->stream, &vcap->ved, 1);
>  	if (ret) {
>  		media_pipeline_stop(entity);
>  		vimc_cap_return_all_buffers(vcap, VB2_BUF_STATE_QUEUED);
> @@ -273,8 +273,7 @@ static void vimc_cap_stop_streaming(struct vb2_queue *vq)
>  {
>  	struct vimc_cap_device *vcap = vb2_get_drv_priv(vq);
>  
> -	/* Disable streaming from the pipe */
> -	vimc_pipeline_s_stream(&vcap->vdev.entity, 0);
> +	vimc_streamer_s_stream(&vcap->stream, &vcap->ved, 0);
>  
>  	/* Stop the media pipeline */
>  	media_pipeline_stop(&vcap->vdev.entity);
> @@ -355,8 +354,8 @@ static void vimc_cap_comp_unbind(struct device *comp, struct device *master,
>  	kfree(vcap);
>  }
>  
> -static void vimc_cap_process_frame(struct vimc_ent_device *ved,
> -				   struct media_pad *sink, const void *frame)
> +static void *vimc_cap_process_frame(struct vimc_ent_device *ved,
> +				    const void *frame)
>  {
>  	struct vimc_cap_device *vcap = container_of(ved, struct vimc_cap_device,
>  						    ved);
> @@ -370,7 +369,7 @@ static void vimc_cap_process_frame(struct vimc_ent_device *ved,
>  					    typeof(*vimc_buf), list);
>  	if (!vimc_buf) {
>  		spin_unlock(&vcap->qlock);
> -		return;
> +		return ERR_PTR(-EAGAIN);
>  	}
>  
>  	/* Remove this entry from the list */
> @@ -391,6 +390,7 @@ static void vimc_cap_process_frame(struct vimc_ent_device *ved,
>  	vb2_set_plane_payload(&vimc_buf->vb2.vb2_buf, 0,
>  			      vcap->format.sizeimage);
>  	vb2_buffer_done(&vimc_buf->vb2.vb2_buf, VB2_BUF_STATE_DONE);
> +	return NULL;
>  }
>  
>  static int vimc_cap_comp_bind(struct device *comp, struct device *master,
> diff --git a/drivers/media/platform/vimc/vimc-common.c b/drivers/media/platform/vimc/vimc-common.c
> index dee1b9dfc4f6..8eb27ac589e2 100644
> --- a/drivers/media/platform/vimc/vimc-common.c
> +++ b/drivers/media/platform/vimc/vimc-common.c
> @@ -207,41 +207,6 @@ const struct vimc_pix_map *vimc_pix_map_by_pixelformat(u32 pixelformat)
>  }
>  EXPORT_SYMBOL_GPL(vimc_pix_map_by_pixelformat);
>  
> -int vimc_propagate_frame(struct media_pad *src, const void *frame)
> -{
> -	struct media_link *link;
> -
> -	if (!(src->flags & MEDIA_PAD_FL_SOURCE))
> -		return -EINVAL;
> -
> -	/* Send this frame to all sink pads that are direct linked */
> -	list_for_each_entry(link, &src->entity->links, list) {
> -		if (link->source == src &&
> -		    (link->flags & MEDIA_LNK_FL_ENABLED)) {
> -			struct vimc_ent_device *ved = NULL;
> -			struct media_entity *entity = link->sink->entity;
> -
> -			if (is_media_entity_v4l2_subdev(entity)) {
> -				struct v4l2_subdev *sd =
> -					container_of(entity, struct v4l2_subdev,
> -						     entity);
> -				ved = v4l2_get_subdevdata(sd);
> -			} else if (is_media_entity_v4l2_video_device(entity)) {
> -				struct video_device *vdev =
> -					container_of(entity,
> -						     struct video_device,
> -						     entity);
> -				ved = video_get_drvdata(vdev);
> -			}
> -			if (ved && ved->process_frame)
> -				ved->process_frame(ved, link->sink, frame);
> -		}
> -	}
> -
> -	return 0;
> -}
> -EXPORT_SYMBOL_GPL(vimc_propagate_frame);
> -
>  /* Helper function to allocate and initialize pads */
>  struct media_pad *vimc_pads_init(u16 num_pads, const unsigned long *pads_flag)
>  {
> @@ -263,6 +228,21 @@ struct media_pad *vimc_pads_init(u16 num_pads, const unsigned long *pads_flag)
>  }
>  EXPORT_SYMBOL_GPL(vimc_pads_init);
>  
> +struct media_entity *vimc_get_source_entity(struct media_entity *ent)

You can use const here:

const struct media_entity *ent

> +{
> +	struct media_pad *pad;
> +	int i;
> +
> +	for (i = 0; i < ent->num_pads; i++) {
> +		if (ent->pads[i].flags & MEDIA_PAD_FL_SOURCE)
> +			continue;
> +		pad = media_entity_remote_pad(&ent->pads[i]);
> +		return pad ? pad->entity : NULL;

Just a suggestion (feel free to take it or not):

		if (ent->pads[i].flags & MEDIA_PAD_FL_SINK) {
			pad = media_entity_remote_pad(&ent->pads[i]);
			return pad ? pad->entity : NULL;
		}

and IMO it is easier to read.

> +	}
> +	return NULL;
> +}
> +EXPORT_SYMBOL_GPL(vimc_get_source_entity);
> +
>  int vimc_pipeline_s_stream(struct media_entity *ent, int enable)
>  {
>  	struct v4l2_subdev *sd;
> diff --git a/drivers/media/platform/vimc/vimc-common.h b/drivers/media/platform/vimc/vimc-common.h
> index 2e9981b18166..1cbafd31ecb0 100644
> --- a/drivers/media/platform/vimc/vimc-common.h
> +++ b/drivers/media/platform/vimc/vimc-common.h
> @@ -113,22 +113,21 @@ struct vimc_pix_map {
>  struct vimc_ent_device {
>  	struct media_entity *ent;
>  	struct media_pad *pads;
> -	void (*process_frame)(struct vimc_ent_device *ved,
> -			      struct media_pad *sink, const void *frame);
> +	void * (*process_frame)(struct vimc_ent_device *ved,
> +				const void *frame);
>  	void (*vdev_get_format)(struct vimc_ent_device *ved,
>  			      struct v4l2_pix_format *fmt);
>  };
>  
>  /**
> - * vimc_propagate_frame - propagate a frame through the topology
> + * vimc_get_source_entity - get the media_entity source of a given media_entity


pads type are either sink or source, not entities.

suggestion:

get the remote entity connected to a sink pad

or:

get the remote entity with a source pad

or:
get the remote entity who owns the source pad in the link

>   *
> - * @src:	the source pad where the frame is being originated
> - * @frame:	the frame to be propagated
> + * @ent:	reference media_entity
>   *
> - * This function will call the process_frame callback from the vimc_ent_device
> - * struct of the nodes directly connected to the @src pad
> + * Helper function that return the media entity which is source from the given
> + * media entity.

s/return/returns

I would also reword this a bit:

Helper function that returns the media entity who owns the source pad
across of an enabled link in @ent.

(but take it with a grain of salt as my English is not that good)

>   */
> -int vimc_propagate_frame(struct media_pad *src, const void *frame);
> +struct media_entity *vimc_get_source_entity(struct media_entity *ent);

This function is only used by the streamer code, so I don't think
putting it in common makes much sense for now (unless you think it might
be useful for latter), so maybe just declaring it static in
vimc-streamer.c is ok.

>  
>  /**
>   * vimc_pads_init - initialize pads
> diff --git a/drivers/media/platform/vimc/vimc-debayer.c b/drivers/media/platform/vimc/vimc-debayer.c
> index 77887f66f323..7d77c63b99d2 100644
> --- a/drivers/media/platform/vimc/vimc-debayer.c
> +++ b/drivers/media/platform/vimc/vimc-debayer.c
> @@ -321,7 +321,6 @@ static void vimc_deb_set_rgb_mbus_fmt_rgb888_1x24(struct vimc_deb_device *vdeb,
>  static int vimc_deb_s_stream(struct v4l2_subdev *sd, int enable)
>  {
>  	struct vimc_deb_device *vdeb = v4l2_get_subdevdata(sd);
> -	int ret;
>  
>  	if (enable) {
>  		const struct vimc_pix_map *vpix;
> @@ -351,22 +350,10 @@ static int vimc_deb_s_stream(struct v4l2_subdev *sd, int enable)
>  		if (!vdeb->src_frame)
>  			return -ENOMEM;
>  
> -		/* Turn the stream on in the subdevices directly connected */
> -		ret = vimc_pipeline_s_stream(&vdeb->sd.entity, 1);
> -		if (ret) {
> -			vfree(vdeb->src_frame);
> -			vdeb->src_frame = NULL;
> -			return ret;
> -		}
>  	} else {
>  		if (!vdeb->src_frame)
>  			return 0;
>  
> -		/* Disable streaming from the pipe */
> -		ret = vimc_pipeline_s_stream(&vdeb->sd.entity, 0);
> -		if (ret)
> -			return ret;
> -
>  		vfree(vdeb->src_frame);
>  		vdeb->src_frame = NULL;
>  	}
> @@ -480,9 +467,8 @@ static void vimc_deb_calc_rgb_sink(struct vimc_deb_device *vdeb,
>  	}
>  }
>  
> -static void vimc_deb_process_frame(struct vimc_ent_device *ved,
> -				   struct media_pad *sink,
> -				   const void *sink_frame)
> +static void *vimc_deb_process_frame(struct vimc_ent_device *ved,
> +				    const void *sink_frame)
>  {
>  	struct vimc_deb_device *vdeb = container_of(ved, struct vimc_deb_device,
>  						    ved);
> @@ -491,7 +477,7 @@ static void vimc_deb_process_frame(struct vimc_ent_device *ved,
>  
>  	/* If the stream in this node is not active, just return */
>  	if (!vdeb->src_frame)
> -		return;
> +		return ERR_PTR(-EINVAL);
>  
>  	for (i = 0; i < vdeb->sink_fmt.height; i++)
>  		for (j = 0; j < vdeb->sink_fmt.width; j++) {
> @@ -499,12 +485,8 @@ static void vimc_deb_process_frame(struct vimc_ent_device *ved,
>  			vdeb->set_rgb_src(vdeb, i, j, rgb);
>  		}
>  
> -	/* Propagate the frame through all source pads */
> -	for (i = 1; i < vdeb->sd.entity.num_pads; i++) {
> -		struct media_pad *pad = &vdeb->sd.entity.pads[i];
> +	return vdeb->src_frame;
>  
> -		vimc_propagate_frame(pad, vdeb->src_frame);
> -	}
>  }
>  
>  static void vimc_deb_comp_unbind(struct device *comp, struct device *master,
> diff --git a/drivers/media/platform/vimc/vimc-scaler.c b/drivers/media/platform/vimc/vimc-scaler.c
> index b0952ee86296..39b2a73dfcc1 100644
> --- a/drivers/media/platform/vimc/vimc-scaler.c
> +++ b/drivers/media/platform/vimc/vimc-scaler.c
> @@ -217,7 +217,6 @@ static const struct v4l2_subdev_pad_ops vimc_sca_pad_ops = {
>  static int vimc_sca_s_stream(struct v4l2_subdev *sd, int enable)
>  {
>  	struct vimc_sca_device *vsca = v4l2_get_subdevdata(sd);
> -	int ret;
>  
>  	if (enable) {
>  		const struct vimc_pix_map *vpix;
> @@ -245,22 +244,10 @@ static int vimc_sca_s_stream(struct v4l2_subdev *sd, int enable)
>  		if (!vsca->src_frame)
>  			return -ENOMEM;
>  
> -		/* Turn the stream on in the subdevices directly connected */
> -		ret = vimc_pipeline_s_stream(&vsca->sd.entity, 1);
> -		if (ret) {
> -			vfree(vsca->src_frame);
> -			vsca->src_frame = NULL;
> -			return ret;
> -		}
>  	} else {
>  		if (!vsca->src_frame)
>  			return 0;
>  
> -		/* Disable streaming from the pipe */
> -		ret = vimc_pipeline_s_stream(&vsca->sd.entity, 0);
> -		if (ret)
> -			return ret;
> -
>  		vfree(vsca->src_frame);
>  		vsca->src_frame = NULL;
>  	}
> @@ -346,26 +333,19 @@ static void vimc_sca_fill_src_frame(const struct vimc_sca_device *const vsca,
>  			vimc_sca_scale_pix(vsca, i, j, sink_frame);
>  }
>  
> -static void vimc_sca_process_frame(struct vimc_ent_device *ved,
> -				   struct media_pad *sink,
> -				   const void *sink_frame)
> +static void *vimc_sca_process_frame(struct vimc_ent_device *ved,
> +				    const void *sink_frame)
>  {
>  	struct vimc_sca_device *vsca = container_of(ved, struct vimc_sca_device,
>  						    ved);
> -	unsigned int i;
>  
>  	/* If the stream in this node is not active, just return */
>  	if (!vsca->src_frame)
> -		return;
> +		return ERR_PTR(-EINVAL);
>  
>  	vimc_sca_fill_src_frame(vsca, sink_frame);
>  
> -	/* Propagate the frame through all source pads */
> -	for (i = 1; i < vsca->sd.entity.num_pads; i++) {
> -		struct media_pad *pad = &vsca->sd.entity.pads[i];
> -
> -		vimc_propagate_frame(pad, vsca->src_frame);
> -	}
> +	return vsca->src_frame;
>  };
>  
>  static void vimc_sca_comp_unbind(struct device *comp, struct device *master,
> diff --git a/drivers/media/platform/vimc/vimc-sensor.c b/drivers/media/platform/vimc/vimc-sensor.c
> index 32ca9c6172b1..93961a1e694f 100644
> --- a/drivers/media/platform/vimc/vimc-sensor.c
> +++ b/drivers/media/platform/vimc/vimc-sensor.c
> @@ -16,8 +16,6 @@
>   */
>  
>  #include <linux/component.h>
> -#include <linux/freezer.h>
> -#include <linux/kthread.h>
>  #include <linux/module.h>
>  #include <linux/mod_devicetable.h>
>  #include <linux/platform_device.h>
> @@ -201,38 +199,27 @@ static const struct v4l2_subdev_pad_ops vimc_sen_pad_ops = {
>  	.set_fmt		= vimc_sen_set_fmt,
>  };
>  
> -static int vimc_sen_tpg_thread(void *data)
> +static void *vimc_sen_process_frame(struct vimc_ent_device *ved,
> +				    const void *sink_frame)
>  {
> -	struct vimc_sen_device *vsen = data;
> -	unsigned int i;
> -
> -	set_freezable();
> -	set_current_state(TASK_UNINTERRUPTIBLE);
> -
> -	for (;;) {
> -		try_to_freeze();
> -		if (kthread_should_stop())
> -			break;
> -
> -		tpg_fill_plane_buffer(&vsen->tpg, 0, 0, vsen->frame);
> +	struct vimc_sen_device *vsen = container_of(ved, struct vimc_sen_device,
> +						    ved);
> +	const struct vimc_pix_map *vpix;
> +	unsigned int frame_size;
>  
> -		/* Send the frame to all source pads */
> -		for (i = 0; i < vsen->sd.entity.num_pads; i++)
> -			vimc_propagate_frame(&vsen->sd.entity.pads[i],
> -					     vsen->frame);
> +	/* Calculate the frame size */
> +	vpix = vimc_pix_map_by_code(vsen->mbus_format.code);
> +	frame_size = vsen->mbus_format.width * vpix->bpp *
> +		     vsen->mbus_format.height;
>  
> -		/* 60 frames per second */
> -		schedule_timeout(HZ/60);
> -	}
> -
> -	return 0;
> +	tpg_fill_plane_buffer(&vsen->tpg, 0, 0, vsen->frame);
> +	return vsen->frame;
>  }
>  
>  static int vimc_sen_s_stream(struct v4l2_subdev *sd, int enable)
>  {
>  	struct vimc_sen_device *vsen =
>  				container_of(sd, struct vimc_sen_device, sd);
> -	int ret;
>  
>  	if (enable) {
>  		const struct vimc_pix_map *vpix;
> @@ -258,26 +245,8 @@ static int vimc_sen_s_stream(struct v4l2_subdev *sd, int enable)
>  		/* configure the test pattern generator */
>  		vimc_sen_tpg_s_format(vsen);
>  
> -		/* Initialize the image generator thread */
> -		vsen->kthread_sen = kthread_run(vimc_sen_tpg_thread, vsen,
> -					"%s-sen", vsen->sd.v4l2_dev->name);
> -		if (IS_ERR(vsen->kthread_sen)) {
> -			dev_err(vsen->dev, "%s: kernel_thread() failed\n",
> -				vsen->sd.name);
> -			vfree(vsen->frame);
> -			vsen->frame = NULL;
> -			return PTR_ERR(vsen->kthread_sen);
> -		}
>  	} else {
> -		if (!vsen->kthread_sen)
> -			return 0;
> -
> -		/* Stop image generator */
> -		ret = kthread_stop(vsen->kthread_sen);
> -		if (ret)
> -			return ret;
>  
> -		vsen->kthread_sen = NULL;
>  		vfree(vsen->frame);
>  		vsen->frame = NULL;
>  		return 0;
> @@ -413,6 +382,7 @@ static int vimc_sen_comp_bind(struct device *comp, struct device *master,
>  	if (ret)
>  		goto err_free_hdl;
>  
> +	vsen->ved.process_frame = vimc_sen_process_frame;
>  	dev_set_drvdata(comp, &vsen->ved);
>  	vsen->dev = comp;
>  
> diff --git a/drivers/media/platform/vimc/vimc-streamer.c b/drivers/media/platform/vimc/vimc-streamer.c
> new file mode 100644
> index 000000000000..f614734538c2
> --- /dev/null
> +++ b/drivers/media/platform/vimc/vimc-streamer.c
> @@ -0,0 +1,176 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * vimc-streamer.c Virtual Media Controller Driver
> + *
> + * Copyright (C) 2018 Lucas A. M. MagalhÃes <lucmaga@xxxxxxxxx>
> + *
> + */
> +
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/freezer.h>
> +#include <linux/kthread.h>
> +
> +#include "vimc-streamer.h"
> +
> +/*
> + * vimc_streamer_pipeline_disable - Disable stream in all ved in stream
> + *
> + * @stream: the pointer to the stream structure with the pipeline to be
> + *	    disabled.
> + *
> + * Calls s_stream to disable the stream in each entity of the pipeline
> + *
> + */
> +static void vimc_streamer_pipeline_disable(struct vimc_stream *stream)
> +{
> +	struct media_entity *entity;
> +	struct v4l2_subdev *sd;
> +
> +	do {
> +		stream->pipe_size--;
> +		entity = stream->ved_pipeline[stream->pipe_size]->ent;
> +		entity = vimc_get_source_entity(entity);
> +		stream->ved_pipeline[stream->pipe_size] = NULL;
> +		/*
> +		 *  This may occur only if the streamer was not correctly
> +		 *  initialized.
> +		 */
> +		if (!entity)
> +			continue;

I don't think this can happen, if so, then there is a bug in
vimc_streamer_pipeline_init()

> +
> +		if (!is_media_entity_v4l2_subdev(entity))
> +			continue;
> +
> +		sd = media_entity_to_v4l2_subdev(entity);
> +		v4l2_subdev_call(sd, video, s_stream, 0);

Just a suggestion, feel free to take it or not:

		if (is_media_entity_v4l2_subdev(entity)) {
			sd = media_entity_to_v4l2_subdev(entity);
			v4l2_subdev_call(sd, video, s_stream, 0);
		}

> +	} while (stream->pipe_size);
> +}
> +
> +/*
> + * vimc_streamer_pipeline_init - initializes the stream structure
> + *
> + * @stream: the pointer to the stream structure to be initialized
> + * @ved:    the pointer to the vimc entity initializing the stream
> + *
> + * Initializes the stream structure. Walks through the entity graph to
> + * construct the pipeline used later on the streamer thread.
> + * Calls s_stream to enable stream in all entities of the pipeline.
> + */
> +static int vimc_streamer_pipeline_init(struct vimc_stream *stream,
> +				struct vimc_ent_device *ved)
> +{
> +	struct vimc_ent_device *source_ved = NULL;

I don't think you need to initialize it to NULL.

> +	struct media_entity *entity;
> +	struct video_device *vdev;
> +	struct v4l2_subdev *sd;
> +	int ret = -EINVAL;
> +
> +	stream->pipe_size = 0;
> +	stream->ved_pipeline[stream->pipe_size++] = ved;
> +
> +	while (stream->pipe_size < VIMC_STREAMER_PIPELINE_MAX_SIZE) {
> +		if (!stream->ved_pipeline[stream->pipe_size-1])
> +			return 0;
> +		entity = stream->ved_pipeline[stream->pipe_size-1]->ent;
> +		entity = vimc_get_source_entity(entity);
> +		if (!entity)
> +			return 0;
> +		if (is_media_entity_v4l2_subdev(entity)) {
> +			sd = media_entity_to_v4l2_subdev(entity);
> +			ret = v4l2_subdev_call(sd, video, s_stream, 1);
> +			if (ret && ret != -ENOIOCTLCMD)
> +				break;
> +			source_ved = v4l2_get_subdevdata(sd);
> +		} else {
> +			vdev = container_of(entity,
> +					    struct video_device,
> +					    entity);
> +			source_ved = video_get_drvdata(vdev);
> +		}
> +
> +		stream->ved_pipeline[stream->pipe_size++] = source_ved;
> +		source_ved = NULL;

You don't need to set it to NULL.

> +	}
> +
> +	/*
> +	 * If an error occur during initialization or the pipeline gets longer

s/occur/occurs

durint the initialization

> +	 * than VIMC_STREAMER_PIPELINE_MAX_SIZE the stream is disabled and
> +	 * return the error code.

it returns

> +	 */
> +	vimc_streamer_pipeline_disable(stream);
> +	return ret;
> +}

vimc_streamer_pipeline_disable() undo what vimc_streamer_pipeline_init()
do, I was thinking maybe to change the name to be clear they are oposite.
Maybe vimc_streamer_pipeline_enable() and vimc_streamer_pipeline_disable() ?

> +
> +static int vimc_streamer_thread(void *data)
> +{
> +	struct vimc_stream *stream = data;
> +	int i;
> +
> +	set_freezable();
> +	set_current_state(TASK_UNINTERRUPTIBLE);
> +
> +	for (;;) {
> +		try_to_freeze();
> +		if (kthread_should_stop())
> +			break;
> +
> +		for (i = stream->pipe_size - 1; i >= 0; i--) {
> +			stream->frame = stream->ved_pipeline[i]->process_frame(
> +					stream->ved_pipeline[i],
> +					stream->frame);
> +			if (!stream->frame)
> +				break;
> +			if (IS_ERR(stream->frame))
> +				break;
> +		}
> +		//wait for 60hz
> +		schedule_timeout(HZ / 60);
> +	}
> +
> +	return 0;
> +}
> +
> +int vimc_streamer_s_stream(struct vimc_stream *stream,
> +			   struct vimc_ent_device *ved,
> +			   int enable)
> +{
> +	int ret;
> +
> +	if (!stream || !ved)
> +		return -EINVAL;
> +
> +	if (enable) {
> +		if (stream->kthread)
> +			return 0;
> +
> +		ret = vimc_streamer_pipeline_init(stream, ved);
> +		if (ret)
> +			return ret;
> +
> +		stream->kthread = kthread_run(vimc_streamer_thread, stream,
> +					      "vimc-streamer thread");
> +
> +		if (IS_ERR(stream->kthread))
> +			return PTR_ERR(stream->kthread);
> +
> +	} else {
> +		if (!stream->kthread)
> +			return 0;
> +
> +		ret = kthread_stop(stream->kthread);
> +		if (ret)
> +			return ret;
> +
> +		stream->kthread = NULL;
> +
> +		vimc_streamer_pipeline_disable(stream);
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vimc_streamer_s_stream);
> +
> +MODULE_DESCRIPTION("Virtual Media Controller Driver (VIMC) Streamer");
> +MODULE_AUTHOR("Lucas A. M. MagalhÃes <lucmaga@xxxxxxxxx>");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/media/platform/vimc/vimc-streamer.h b/drivers/media/platform/vimc/vimc-streamer.h
> new file mode 100644
> index 000000000000..752af2e2d5a2
> --- /dev/null
> +++ b/drivers/media/platform/vimc/vimc-streamer.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * vimc-streamer.h Virtual Media Controller Driver
> + *
> + * Copyright (C) 2018 Lucas A. M. MagalhÃes <lucmaga@xxxxxxxxx>
> + *
> + */
> +
> +#ifndef _VIMC_STREAMER_H_
> +#define _VIMC_STREAMER_H_
> +
> +#include <media/media-device.h>
> +
> +#include "vimc-common.h"
> +
> +#define VIMC_STREAMER_PIPELINE_MAX_SIZE 16
> +
> +struct vimc_stream {
> +	struct media_pipeline pipe;
> +	struct vimc_ent_device *ved_pipeline[VIMC_STREAMER_PIPELINE_MAX_SIZE];
> +	unsigned int pipe_size;
> +	u8 *frame;
> +	struct task_struct *kthread;
> +};
> +
> +/**
> + * vimc_streamer_s_streamer - start/stop the stream
> + *
> + * @stream:	the pointer to the stream to start or stop
> + * @ved:	The last entity of the streamer pipeline
> + * @enable:	any non-zero number start the stream, zero stop
> + *
> + */
> +int vimc_streamer_s_stream(struct vimc_stream *stream,
> +			   struct vimc_ent_device *ved,
> +			   int enable);
> +
> +#endif  //_VIMC_STREAMER_H_
> 

Regards,
Helen