Re: [PATCH v7 1/2] uvcvideo: send a control event when a Control Change interrupt arrives

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Guennadi,

Thank you for the patch.

On Friday, 23 March 2018 11:24:00 EET Laurent Pinchart wrote:
> From: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> 
> UVC defines a method of handling asynchronous controls, which sends a
> USB packet over the interrupt pipe. This patch implements support for
> such packets by sending a control event to the user. Since this can
> involve USB traffic and, therefore, scheduling, this has to be done
> in a work queue.
> 
> Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c   | 166 ++++++++++++++++++++++++++++++----
>  drivers/media/usb/uvc/uvc_status.c | 111 ++++++++++++++++++++++---
>  drivers/media/usb/uvc/uvc_v4l2.c   |   4 +-
>  drivers/media/usb/uvc/uvcvideo.h   |  15 +++-
>  include/uapi/linux/uvcvideo.h      |   2 +
>  5 files changed, 269 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c
> b/drivers/media/usb/uvc/uvc_ctrl.c index 4042cbdb721b..f4773c56438c 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -20,6 +20,7 @@
>  #include <linux/videodev2.h>
>  #include <linux/vmalloc.h>
>  #include <linux/wait.h>
> +#include <linux/workqueue.h>
>  #include <linux/atomic.h>
>  #include <media/v4l2-ctrls.h>
> 
> @@ -1222,30 +1223,134 @@ static void uvc_ctrl_send_event(struct uvc_fh
> *handle, {
>  	struct v4l2_subscribed_event *sev;
>  	struct v4l2_event ev;
> +	bool autoupdate;
> 
>  	if (list_empty(&mapping->ev_subs))
>  		return;
> 
> +	if (!handle) {

In which circumstances does this happen ? Is it when the device reports a 
control change event without an prior control set ? Have you seen that 
happening in practice ?

> +		autoupdate = true;
> +		sev = list_first_entry(&mapping->ev_subs,
> +				       struct v4l2_subscribed_event, node);
> +		handle = container_of(sev->fh, struct uvc_fh, vfh);

There's a check below that guards against sev->fh being NULL. Could sev->fh be 
NULL here ?

> +	} else {
> +		autoupdate = false;
> +	}
> +
>  	uvc_ctrl_fill_event(handle->chain, &ev, ctrl, mapping, value, changes);
> 
>  	list_for_each_entry(sev, &mapping->ev_subs, node) {
>  		if (sev->fh && (sev->fh != &handle->vfh ||
>  		    (sev->flags & V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK) ||
> -		    (changes & V4L2_EVENT_CTRL_CH_FLAGS)))
> +		    (changes & V4L2_EVENT_CTRL_CH_FLAGS) || autoupdate))
>  			v4l2_event_queue_fh(sev->fh, &ev);
>  	}
>  }
> 
> -static void uvc_ctrl_send_slave_event(struct uvc_fh *handle,
> -	struct uvc_control *master, u32 slave_id,
> -	const struct v4l2_ext_control *xctrls, unsigned int xctrls_count)
> +static void __uvc_ctrl_send_slave_event(struct uvc_fh *handle,
> +				struct uvc_control *master, u32 slave_id)
>  {
>  	struct uvc_control_mapping *mapping = NULL;
>  	struct uvc_control *ctrl = NULL;
>  	u32 changes = V4L2_EVENT_CTRL_CH_FLAGS;
> -	unsigned int i;
>  	s32 val = 0;
> 
> +	__uvc_find_control(master->entity, slave_id, &mapping, &ctrl, 0);
> +	if (ctrl == NULL)
> +		return;
> +
> +	if (__uvc_ctrl_get(handle->chain, ctrl, mapping, &val) == 0)
> +		changes |= V4L2_EVENT_CTRL_CH_VALUE;
> +
> +	uvc_ctrl_send_event(handle, ctrl, mapping, val, changes);
> +}
> +
> +static void uvc_ctrl_status_event_work(struct work_struct *work)
> +{
> +	struct uvc_device *dev = container_of(work, struct uvc_device,
> +					      async_ctrl.work);
> +	struct uvc_video_chain *chain;
> +	struct uvc_ctrl_work *w = &dev->async_ctrl;
> +	struct uvc_control_mapping *mapping;
> +	struct uvc_control *ctrl;
> +	struct uvc_fh *handle;
> +	unsigned int i;
> +	u8 *data;
> +
> +	spin_lock_irq(&w->lock);
> +	data = w->data;
> +	w->data = NULL;
> +	chain = w->chain;
> +	ctrl = w->ctrl;
> +	handle = ctrl->handle;
> +	ctrl->handle = NULL;
> +	spin_unlock_irq(&w->lock);
> +
> +	if (mutex_lock_interruptible(&chain->ctrl_mutex))
> +		goto free;

This will result in the event being lost, which isn't very nice (see below for 
additional comments on this topic). Can't we use mutex_lock() ?

> +
> +	list_for_each_entry(mapping, &ctrl->info.mappings, list) {
> +		s32 value = mapping->get(mapping, UVC_GET_CUR, data);
> +
> +		for (i = 0; i < ARRAY_SIZE(mapping->slave_ids); ++i) {
> +			if (!mapping->slave_ids[i])
> +				break;
> +
> +			__uvc_ctrl_send_slave_event(handle, ctrl,
> +						    mapping->slave_ids[i]);
> +		}
> +
> +		if (mapping->v4l2_type == V4L2_CTRL_TYPE_MENU) {
> +			struct uvc_menu_info *menu = mapping->menu_info;
> +			unsigned int i;
> +
> +			for (i = 0; i < mapping->menu_count; ++i, ++menu)
> +				if (menu->value == value) {
> +					value = i;
> +					break;
> +				}
> +		}

Would this be useful to move the mapping->get() and menu control handling code 
out of __uvc_ctrl_get() into a __uvc_ctrl_get_value() function and call it 
here ?

> +		uvc_ctrl_send_event(handle, ctrl, mapping, value,
> +				    V4L2_EVENT_CTRL_CH_VALUE);
> +	}
> +
> +	mutex_unlock(&chain->ctrl_mutex);
> +
> +free:
> +	kfree(data);
> +}
> +
> +void uvc_ctrl_status_event(struct uvc_video_chain *chain,
> +			   struct uvc_control *ctrl, u8 *data, size_t len)
> +{
> +	struct uvc_device *dev = chain->dev;
> +	struct uvc_ctrl_work *w = &dev->async_ctrl;
> +
> +	if (list_empty(&ctrl->info.mappings))
> +		return;
> +
> +	spin_lock(&w->lock);
> +	if (w->data)
> +		/* A previous event work hasn't run yet, we lose 1 event */
> +		kfree(w->data);

I really don't like losing events :/ 

> +	w->data = kmalloc(len, GFP_ATOMIC);

GFP_ATOMIC allocation isn't very nice either.

How about if we instead delayed resubmitting the status URB until the event is 
fully processed by the work queue ? That way we wouldn't lose events, we 
wouldn't need memory allocation in atomic context, and if the work queue 
becomes a bottleneck we could even queue multiple status URBs and easily add 
them to a list for processing by the work queue.

> +	if (w->data) {
> +		memcpy(w->data, data, len);
> +		w->chain = chain;
> +		w->ctrl = ctrl;
> +		schedule_work(&w->work);
> +	}
> +	spin_unlock(&w->lock);
> +}
> +
> +static void uvc_ctrl_send_slave_event(struct uvc_fh *handle,
> +	struct uvc_control *master, u32 slave_id,
> +	const struct v4l2_ext_control *xctrls, unsigned int xctrls_count)
> +{
> +	unsigned int i;
> +
>  	/*
>  	 * We can skip sending an event for the slave if the slave
>  	 * is being modified in the same transaction.
> @@ -1255,14 +1360,7 @@ static void uvc_ctrl_send_slave_event(struct uvc_fh
> *handle, return;
>  	}
> 
> -	__uvc_find_control(master->entity, slave_id, &mapping, &ctrl, 0);
> -	if (ctrl == NULL)
> -		return;
> -
> -	if (__uvc_ctrl_get(handle->chain, ctrl, mapping, &val) == 0)
> -		changes |= V4L2_EVENT_CTRL_CH_VALUE;
> -
> -	uvc_ctrl_send_event(handle, ctrl, mapping, val, changes);
> +	__uvc_ctrl_send_slave_event(handle, master, slave_id);
>  }
> 
>  static void uvc_ctrl_send_events(struct uvc_fh *handle,
> @@ -1277,6 +1375,10 @@ static void uvc_ctrl_send_events(struct uvc_fh
> *handle, for (i = 0; i < xctrls_count; ++i) {
>  		ctrl = uvc_find_control(handle->chain, xctrls[i].id, &mapping);
> 
> +		if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS)
> +			/* Notification will be sent from an Interrupt event */

Nitpicking, could you add a period at the end of sentences to match the 
comment style in the driver ?

> +			continue;
> +
>  		for (j = 0; j < ARRAY_SIZE(mapping->slave_ids); ++j) {
>  			if (!mapping->slave_ids[j])
>  				break;
> @@ -1472,9 +1574,10 @@ int uvc_ctrl_get(struct uvc_video_chain *chain,
>  	return __uvc_ctrl_get(chain, ctrl, mapping, &xctrl->value);
>  }
> 
> -int uvc_ctrl_set(struct uvc_video_chain *chain,
> +int uvc_ctrl_set(struct uvc_fh *handle,
>  	struct v4l2_ext_control *xctrl)
>  {
> +	struct uvc_video_chain *chain = handle->chain;
>  	struct uvc_control *ctrl;
>  	struct uvc_control_mapping *mapping;
>  	s32 value;
> @@ -1488,6 +1591,25 @@ int uvc_ctrl_set(struct uvc_video_chain *chain,
>  		return -EINVAL;
>  	if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR))
>  		return -EACCES;
> +	if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS) {
> +		if (ctrl->handle)
> +			/*
> +			 * We have already sent this control to the camera
> +			 * recently and are currently waiting for a completion
> +			 * notification. The camera might already have completed
> +			 * its processing and is ready to accept a new control
> +			 * or it's still busy processing. If we send a new
> +			 * instance of this control now, in the former case the
> +			 * camera will process this one too and we'll get
> +			 * completions for both, but we will only deliver an
> +			 * event for one of them back to the user. In the latter
> +			 * case the camera will reply with a STALL. It's easier
> +			 * and more reliable to return an error now and let the
> +			 * user retry.
> +			 */
> +			return -EBUSY;
> +		ctrl->handle = handle;

This part worries me. If the control change event isn't received for any 
reason (such as a buggy device for instance, or uvc_ctrl_status_event() being 
called with the previous event not processed yet), the control will stay busy 
forever.

I see two approaches to fix this. One would be to forward all received control 
change events to all file handles unconditionally and remove the handle field 
from the uvc_control structure. Another one would be to add a timeout, storing 
the time at which the control has been set in the uvc_control structure, and 
checking whether the time difference exceeds a fixed timeout here. We could 
also combine the two, replacing the handle field with a timestamp field.

Please keep in mind if trying this out that simply storing jiffies as a 
timestamp might cause counter overflow issues if the control is set, no event 
is ever received, and a second control set happens much later after one (or 
multiple) jiffies wraparounds. We could end up returning -EBUSY incorrectly. 
That might not be a real issue given the size of the jiffies counter though,  
I'll let you double-check.

> +	}
> 
>  	/* Clamp out of range values. */
>  	switch (mapping->v4l2_type) {
> @@ -1612,7 +1734,9 @@ static int uvc_ctrl_get_flags(struct uvc_device *dev,
>  			    |  (data[0] & UVC_CONTROL_CAP_SET ?
>  				UVC_CTRL_FLAG_SET_CUR : 0)
>  			    |  (data[0] & UVC_CONTROL_CAP_AUTOUPDATE ?
> -				UVC_CTRL_FLAG_AUTO_UPDATE : 0);
> +				UVC_CTRL_FLAG_AUTO_UPDATE : 0)
> +			    |  (data[0] & UVC_CONTROL_CAP_ASYNCHRONOUS ?
> +				UVC_CTRL_FLAG_ASYNCHRONOUS : 0);
> 
>  	kfree(data);
>  	return ret;
> @@ -2158,6 +2282,13 @@ static void uvc_ctrl_init_ctrl(struct uvc_device
> *dev, struct uvc_control *ctrl) if (!ctrl->initialized)
>  		return;
> 
> +	/* Temporarily abuse DATA_CURRENT buffer to avoid 1 byte allocation */
> +	if (!uvc_query_ctrl(dev, UVC_GET_INFO, ctrl->entity->id,
> +			    dev->intfnum, info->selector,
> +			    uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT), 1) &&
> +	    uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT)[0] & 0x10)
> +		ctrl->info.flags |= UVC_CTRL_FLAG_ASYNCHRONOUS;

I think this isn't needed anymore as the uvc_ctrl_add_info() function now 
calls uvc_ctrl_get_flags() to update the flags. Could you please confirm ?

>  	for (; mapping < mend; ++mapping) {
>  		if (uvc_entity_match_guid(ctrl->entity, mapping->entity) &&
>  		    ctrl->info.selector == mapping->selector)
> @@ -2173,6 +2304,9 @@ int uvc_ctrl_init_device(struct uvc_device *dev)
>  	struct uvc_entity *entity;
>  	unsigned int i;
> 
> +	spin_lock_init(&dev->async_ctrl.lock);
> +	INIT_WORK(&dev->async_ctrl.work, uvc_ctrl_status_event_work);
> +
>  	/* Walk the entities list and instantiate controls */
>  	list_for_each_entry(entity, &dev->entities, list) {
>  		struct uvc_control *ctrl;
> @@ -2241,6 +2375,8 @@ void uvc_ctrl_cleanup_device(struct uvc_device *dev)
>  	struct uvc_entity *entity;
>  	unsigned int i;
> 
> +	cancel_work_sync(&dev->async_ctrl.work);
> +
>  	/* Free controls and control mappings for all entities. */
>  	list_for_each_entry(entity, &dev->entities, list) {
>  		for (i = 0; i < entity->ncontrols; ++i) {
> diff --git a/drivers/media/usb/uvc/uvc_status.c
> b/drivers/media/usb/uvc/uvc_status.c index 7b710410584a..d1d83aed6a1d
> 100644
> --- a/drivers/media/usb/uvc/uvc_status.c
> +++ b/drivers/media/usb/uvc/uvc_status.c
> @@ -78,7 +78,24 @@ static void uvc_input_report_key(struct uvc_device *dev,
> unsigned int code, /*
> --------------------------------------------------------------------------
> * Status interrupt endpoint
>   */
> -static void uvc_event_streaming(struct uvc_device *dev, u8 *data, int len)
> +struct uvc_streaming_status {
> +	u8	bStatusType;
> +	u8	bOriginator;
> +	u8	bEvent;
> +	u8	bValue[];
> +} __packed;
> +
> +struct uvc_control_status {
> +	u8	bStatusType;
> +	u8	bOriginator;
> +	u8	bEvent;
> +	u8	bSelector;
> +	u8	bAttribute;
> +	u8	bValue[];
> +} __packed;
> +
> +static void uvc_event_streaming(struct uvc_device *dev,
> +				struct uvc_streaming_status *status, int len)
>  {
>  	if (len < 3) {
>  		uvc_trace(UVC_TRACE_STATUS, "Invalid streaming status event "
> @@ -86,31 +103,101 @@ static void uvc_event_streaming(struct uvc_device
> *dev, u8 *data, int len) return;
>  	}
> 
> -	if (data[2] == 0) {
> +	if (status->bEvent == 0) {
>  		if (len < 4)
>  			return;
>  		uvc_trace(UVC_TRACE_STATUS, "Button (intf %u) %s len %d\n",
> -			data[1], data[3] ? "pressed" : "released", len);
> -		uvc_input_report_key(dev, KEY_CAMERA, data[3]);
> +			  status->bOriginator,
> +			  status->bValue[0] ? "pressed" : "released", len);
> +		uvc_input_report_key(dev, KEY_CAMERA, status->bValue[0]);
>  	} else {
>  		uvc_trace(UVC_TRACE_STATUS,
>  			  "Stream %u error event %02x len %d.\n",
> -			  data[1], data[2], len);
> +			  status->bOriginator, status->bEvent, len);
>  	}
>  }
> 
> -static void uvc_event_control(struct uvc_device *dev, u8 *data, int len)
> +#define UVC_CTRL_VALUE_CHANGE	0
> +#define UVC_CTRL_INFO_CHANGE	1
> +#define UVC_CTRL_FAILURE_CHANGE	2
> +#define UVC_CTRL_MIN_CHANGE	3
> +#define UVC_CTRL_MAX_CHANGE	4
> +
> +static struct uvc_control *uvc_event_entity_ctrl(struct uvc_entity *entity,
> +					       u8 selector)

Should this be named uvc_event_entity_find_ctrl() ?

> +{
> +	struct uvc_control *ctrl;
> +	unsigned int i;
> +
> +	for (i = 0, ctrl = entity->controls; i < entity->ncontrols; i++, ctrl++)
> +		if (ctrl->info.selector == selector)
> +			return ctrl;
> +
> +	return NULL;
> +}
> +
> +static struct uvc_control *uvc_event_find_ctrl(struct uvc_device *dev,
> +					struct uvc_control_status *status,
> +					struct uvc_video_chain **chain)
> +{
> +	list_for_each_entry((*chain), &dev->chains, list) {

Do you need parentheses around *chain ?

> +		struct uvc_entity *entity;
> +		struct uvc_control *ctrl;
> +
> +		list_for_each_entry(entity, &(*chain)->entities, chain) {
> +			if (entity->id == status->bOriginator) {

If you invert the check here with

			if (entity->id == status->bOriginator)
				continue;

you'll gain one level of indentation and you might be able to inline 
uvc_event_entity_ctrl(). Up to you.

> +				ctrl = uvc_event_entity_ctrl(entity,
> +							     status->bSelector);
> +				/*
> +				 * Some buggy cameras send asynchronous Control
> +				 * Change events for control, other than the
> +				 * ones, that had been changed, even though the
> +				 * AutoUpdate flag isn't set for the control.
> +				 */

That's lots of commas, I'm not sure what you mean here. Are there cameras that 
send event for controls that haven't changed ? Or cameras that send events for 
controls that don't have the auto-update flag set ? Do you know what cameras 
are affected ?

> +				if (ctrl && (!ctrl->handle ||
> +					     ctrl->handle->chain == *chain))
> +					return ctrl;
> +			}
> +		}
> +	}
> +
> +	return NULL;
> +}
> +
> +static void uvc_event_control(struct uvc_device *dev,
> +			      struct uvc_control_status *status, int len)

While at it you can make the status pointer const.

>  {
> -	char *attrs[3] = { "value", "info", "failure" };
> +	struct uvc_video_chain *chain;
> +	struct uvc_control *ctrl;
> +	char *attrs[] = { "value", "info", "failure", "min", "max" };

You can also make these static const (and while at it could you please move 
them before the other two variables ?).

> 
> -	if (len < 6 || data[2] != 0 || data[4] > 2) {
> +	if (len < 6 || status->bEvent != 0 ||
> +	    status->bAttribute >= ARRAY_SIZE(attrs)) {
>  		uvc_trace(UVC_TRACE_STATUS, "Invalid control status event "
>  				"received.\n");
>  		return;

The min and max events are only defined in UVC 1.5 but I suppose there's no 
need to check for the UVC version here, it won't hurt to handle them on UVC 
1.1 as well as they should not occur.

>  	}
> 
>  	uvc_trace(UVC_TRACE_STATUS, "Control %u/%u %s change len %d.\n",
> -		data[1], data[3], attrs[data[4]], len);
> +		  status->bOriginator, status->bSelector,
> +		  attrs[status->bAttribute], len);
> +
> +	/* Find the control. */
> +	ctrl = uvc_event_find_ctrl(dev, status, &chain);
> +	if (!ctrl)
> +		return;
> +
> +	switch (status->bAttribute) {
> +	case UVC_CTRL_VALUE_CHANGE:
> +		uvc_ctrl_status_event(chain, ctrl, status->bValue, len -
> +				      offsetof(struct uvc_control_status, bValue));
> +		break;

How about a blank line here ?

> +	case UVC_CTRL_INFO_CHANGE:
> +	case UVC_CTRL_FAILURE_CHANGE:
> +	case UVC_CTRL_MIN_CHANGE:
> +	case UVC_CTRL_MAX_CHANGE:
> +		break;
> +	}
>  }
> 
>  static void uvc_status_complete(struct urb *urb)
> @@ -139,11 +226,13 @@ static void uvc_status_complete(struct urb *urb)
>  	if (len > 0) {
>  		switch (dev->status[0] & 0x0f) {
>  		case UVC_STATUS_TYPE_CONTROL:
> -			uvc_event_control(dev, dev->status, len);
> +			uvc_event_control(dev,
> +				(struct uvc_control_status *)dev->status, len);

Is dev->status guaranteed to be aligned properly so that no unaligned access 
fault can occur when dereferencing memory through the uvc_control_status and 
uvc_streaming_status structures ? Unaligned access are the reason why UVC 
descriptors are parsed manually instead of through a structure.
>  			break;
> 
>  		case UVC_STATUS_TYPE_STREAMING:
> -			uvc_event_streaming(dev, dev->status, len);
> +			uvc_event_streaming(dev,
> +				(struct uvc_streaming_status *)dev->status, len);
>  			break;
> 
>  		default:
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c
> b/drivers/media/usb/uvc/uvc_v4l2.c index 818a4369a51a..55f973eb16eb 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -994,7 +994,7 @@ static int uvc_ioctl_s_ctrl(struct file *file, void *fh,
> if (ret < 0)
>  		return ret;
> 
> -	ret = uvc_ctrl_set(chain, &xctrl);
> +	ret = uvc_ctrl_set(handle, &xctrl);
>  	if (ret < 0) {
>  		uvc_ctrl_rollback(handle);
>  		return ret;
> @@ -1069,7 +1069,7 @@ static int uvc_ioctl_s_try_ext_ctrls(struct uvc_fh
> *handle, return ret;
> 
>  	for (i = 0; i < ctrls->count; ++ctrl, ++i) {
> -		ret = uvc_ctrl_set(chain, ctrl);
> +		ret = uvc_ctrl_set(handle, ctrl);
>  		if (ret < 0) {
>  			uvc_ctrl_rollback(handle);
>  			ctrls->error_idx = commit ? ctrls->count : i;
> diff --git a/drivers/media/usb/uvc/uvcvideo.h
> b/drivers/media/usb/uvc/uvcvideo.h index 6b955e0dd956..483182fe1b4d 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -12,6 +12,7 @@
>  #include <linux/usb/video.h>
>  #include <linux/uvcvideo.h>
>  #include <linux/videodev2.h>
> +#include <linux/workqueue.h>
>  #include <media/media-device.h>
>  #include <media/v4l2-device.h>
>  #include <media/v4l2-event.h>
> @@ -259,6 +260,8 @@ struct uvc_control {
>  	   initialized:1;
> 
>  	u8 *uvc_data;
> +
> +	struct uvc_fh *handle;	/* Used for asynchronous event delivery */
>  };
> 
>  struct uvc_format_desc {
> @@ -603,6 +606,14 @@ struct uvc_device {
>  	u8 *status;
>  	struct input_dev *input;
>  	char input_phys[64];
> +
> +	struct uvc_ctrl_work {
> +		struct work_struct work;
> +		struct uvc_video_chain *chain;
> +		struct uvc_control *ctrl;
> +		spinlock_t lock;
> +		void *data;
> +	} async_ctrl;
>  };
> 
>  enum uvc_handle_state {
> @@ -756,6 +767,8 @@ int uvc_ctrl_add_mapping(struct uvc_video_chain *chain,
>  int uvc_ctrl_init_device(struct uvc_device *dev);
>  void uvc_ctrl_cleanup_device(struct uvc_device *dev);
>  int uvc_ctrl_restore_values(struct uvc_device *dev);
> +void uvc_ctrl_status_event(struct uvc_video_chain *chain,
> +			   struct uvc_control *ctrl, u8 *data, size_t len);
> 
>  int uvc_ctrl_begin(struct uvc_video_chain *chain);
>  int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
> @@ -773,7 +786,7 @@ static inline int uvc_ctrl_rollback(struct uvc_fh
> *handle) }
> 
>  int uvc_ctrl_get(struct uvc_video_chain *chain, struct v4l2_ext_control
> *xctrl); -int uvc_ctrl_set(struct uvc_video_chain *chain, struct
> v4l2_ext_control *xctrl); +int uvc_ctrl_set(struct uvc_fh *handle, struct
> v4l2_ext_control *xctrl);
> 
>  int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
>  		      struct uvc_xu_control_query *xqry);
> diff --git a/include/uapi/linux/uvcvideo.h b/include/uapi/linux/uvcvideo.h
> index 020714d2c5bd..f80f05b3c423 100644
> --- a/include/uapi/linux/uvcvideo.h
> +++ b/include/uapi/linux/uvcvideo.h
> @@ -28,6 +28,8 @@
>  #define UVC_CTRL_FLAG_RESTORE		(1 << 6)
>  /* Control can be updated by the camera. */
>  #define UVC_CTRL_FLAG_AUTO_UPDATE	(1 << 7)
> +/* Control supports asynchronous reporting */
> +#define UVC_CTRL_FLAG_ASYNCHRONOUS	(1 << 8)
> 
>  #define UVC_CTRL_FLAG_GET_RANGE \
>  	(UVC_CTRL_FLAG_GET_CUR | UVC_CTRL_FLAG_GET_MIN | \

-- 
Regards,

Laurent Pinchart