Re: [PATCH v9] uvcvideo: send a control event when a Control Change interrupt arrives

Laurent Pinchart
2018-07-26T13:40:55Z

Hi Guennadi,

Thank you for the patch.

On Thursday, 26 July 2018 11:17:53 EEST Guennadi Liakhovetski wrote:
> From: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
>
> 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>

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

applied to my tree and pushed to the uvc/next branch.

> ---
>
> v9:
> - multiple optimisations and style improvements from Laurent - thanks
> - avoid the handle rewriting race at least in cases, when the user only
> sends a new control after receiving an event for the previous one
>
> Laurent, you added a couple of comments, using DocBook markup like
> "@param" but you didn't mark those comments for DocBook processing with
> "/**" - I don't care that much, just wanted to check, that that was
> intentional.

Yes, it's not worth compiling that as kerneldoc, I just wanted to mark
references to variable names for clarity.

> drivers/media/usb/uvc/uvc_ctrl.c | 211
> ++++++++++++++++++++++++++++--------- drivers/media/usb/uvc/uvc_status.c |
> 121 ++++++++++++++++++---
> drivers/media/usb/uvc/uvc_v4l2.c | 4 +-
> drivers/media/usb/uvc/uvcvideo.h | 15 ++-
> include/uapi/linux/uvcvideo.h | 2 +
> 5 files changed, 286 insertions(+), 67 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c
> b/drivers/media/usb/uvc/uvc_ctrl.c index 2a213c8..ddd069b 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>
>
> @@ -971,12 +972,30 @@ static int uvc_ctrl_populate_cache(struct
> uvc_video_chain *chain, return 0;
> }
>
> +static s32 __uvc_ctrl_get_value(struct uvc_control_mapping *mapping,
> + const u8 *data)
> +{
> + s32 value = mapping->get(mapping, UVC_GET_CUR, data);
> +
> + 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;
> + }
> + }
> + }
> +
> + return value;
> +}
> +
> static int __uvc_ctrl_get(struct uvc_video_chain *chain,
> struct uvc_control *ctrl, struct uvc_control_mapping *mapping,
> s32 *value)
> {
> - struct uvc_menu_info *menu;
> - unsigned int i;
> int ret;
>
> if ((ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR) == 0)
> @@ -993,18 +1012,8 @@ static int __uvc_ctrl_get(struct uvc_video_chain
> *chain, ctrl->loaded = 1;
> }
>
> - *value = mapping->get(mapping, UVC_GET_CUR,
> - uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT));
> -
> - if (mapping->v4l2_type == V4L2_CTRL_TYPE_MENU) {
> - menu = mapping->menu_info;
> - for (i = 0; i < mapping->menu_count; ++i, ++menu) {
> - if (menu->value == *value) {
> - *value = i;
> - break;
> - }
> - }
> - }
> + *value = __uvc_ctrl_get_value(mapping,
> + uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT));
>
> return 0;
> }
> @@ -1216,53 +1225,135 @@ static void uvc_ctrl_fill_event(struct
> uvc_video_chain *chain, ev->u.ctrl.default_value = v4l2_ctrl.default_value;
> }
>
> -static void uvc_ctrl_send_event(struct uvc_fh *handle,
> - struct uvc_control *ctrl, struct uvc_control_mapping *mapping,
> - s32 value, u32 changes)
> +/*
> + * Send control change events to all subscribers for the @ctrl control. By
> + * default the subscriber that generated the event, as identified by
> @handle, + * is not notified unless it has set the
> V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK flag. + * @handle can be NULL for
> asynchronous events related to auto-update controls, + * in which case all
> subscribers are notified.
> + */
> +static void uvc_ctrl_send_event(struct uvc_video_chain *chain,
> + struct uvc_fh *handle, struct uvc_control *ctrl,
> + struct uvc_control_mapping *mapping, s32 value, u32 changes)
> {
> + struct v4l2_fh *originator = handle ? &handle->vfh : NULL;
> struct v4l2_subscribed_event *sev;
> struct v4l2_event ev;
>
> if (list_empty(&mapping->ev_subs))
> return;
>
> - uvc_ctrl_fill_event(handle->chain, &ev, ctrl, mapping, value, changes);
> + uvc_ctrl_fill_event(chain, &ev, ctrl, mapping, value, changes);
>
> list_for_each_entry(sev, &mapping->ev_subs, node) {
> - if (sev->fh != &handle->vfh ||
> + if (sev->fh != originator ||
> (sev->flags & V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK) ||
> (changes & V4L2_EVENT_CTRL_CH_FLAGS))
> 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)
> +/*
> + * Send control change events for the slave of the @master control
> identified + * by the V4L2 ID @slave_id. The @handle identifies the event
> subscriber that + * generated the event and may be NULL for auto-update
> events.
> + */
> +static void uvc_ctrl_send_slave_event(struct uvc_video_chain *chain,
> + 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;
>
> - /*
> - * We can skip sending an event for the slave if the slave
> - * is being modified in the same transaction.
> - */
> - for (i = 0; i < xctrls_count; i++) {
> - if (xctrls[i].id == slave_id)
> - 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)
> + if (__uvc_ctrl_get(chain, ctrl, mapping, &val) == 0)
> changes |= V4L2_EVENT_CTRL_CH_VALUE;
>
> - uvc_ctrl_send_event(handle, ctrl, mapping, val, changes);
> + uvc_ctrl_send_event(chain, 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_ctrl_work *w = &dev->async_ctrl;
> + struct uvc_video_chain *chain = w->chain;
> + struct uvc_control_mapping *mapping;
> + struct uvc_control *ctrl = w->ctrl;
> + struct uvc_fh *handle;
> + unsigned int i;
> + int ret;
> +
> + mutex_lock(&chain->ctrl_mutex);
> +
> + handle = ctrl->handle;
> + ctrl->handle = NULL;
> +
> + list_for_each_entry(mapping, &ctrl->info.mappings, list) {
> + s32 value = __uvc_ctrl_get_value(mapping, w->data);
> +
> + /*
> + * handle may be NULL here if the device sends auto-update
> + * events without a prior related control set from userspace.
> + */
> + for (i = 0; i < ARRAY_SIZE(mapping->slave_ids); ++i) {
> + if (!mapping->slave_ids[i])
> + break;
> +
> + uvc_ctrl_send_slave_event(chain, handle, ctrl,
> + mapping->slave_ids[i]);
> + }
> +
> + uvc_ctrl_send_event(chain, handle, ctrl, mapping, value,
> + V4L2_EVENT_CTRL_CH_VALUE);
> + }
> +
> + mutex_unlock(&chain->ctrl_mutex);
> +
> + /* Resubmit the URB. */
> + w->urb->interval = dev->int_ep->desc.bInterval;
> + ret = usb_submit_urb(w->urb, GFP_KERNEL);
> + if (ret < 0)
> + uvc_printk(KERN_ERR, "Failed to resubmit status URB (%d).\n",
> + ret);
> +}
> +
> +bool uvc_ctrl_status_event(struct urb *urb, struct uvc_video_chain *chain,
> + struct uvc_control *ctrl, const u8 *data)
> +{
> + struct uvc_device *dev = chain->dev;
> + struct uvc_ctrl_work *w = &dev->async_ctrl;
> +
> + if (list_empty(&ctrl->info.mappings)) {
> + ctrl->handle = NULL;
> + return false;
> + }
> +
> + w->data = data;
> + w->urb = urb;
> + w->chain = chain;
> + w->ctrl = ctrl;
> +
> + schedule_work(&w->work);
> +
> + return true;
> +}
> +
> +static bool uvc_ctrl_xctrls_has_control(const struct v4l2_ext_control
> *xctrls, + unsigned int xctrls_count, u32 id)
> +{
> + unsigned int i;
> +
> + for (i = 0; i < xctrls_count; ++i) {
> + if (xctrls[i].id == id)
> + return true;
> + }
> +
> + return false;
> }
>
> static void uvc_ctrl_send_events(struct uvc_fh *handle,
> @@ -1277,29 +1368,39 @@ 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. */
> + continue;
> +
> for (j = 0; j < ARRAY_SIZE(mapping->slave_ids); ++j) {
> - if (!mapping->slave_ids[j])
> + u32 slave_id = mapping->slave_ids[j];
> +
> + if (!slave_id)
> break;
> - uvc_ctrl_send_slave_event(handle, ctrl,
> - mapping->slave_ids[j],
> - xctrls, xctrls_count);
> +
> + /*
> + * We can skip sending an event for the slave if the
> + * slave is being modified in the same transaction.
> + */
> + if (uvc_ctrl_xctrls_has_control(xctrls, xctrls_count,
> + slave_id))
> + continue;
> +
> + uvc_ctrl_send_slave_event(handle->chain, handle, ctrl,
> + slave_id);
> }
>
> /*
> * If the master is being modified in the same transaction
> * flags may change too.
> */
> - if (mapping->master_id) {
> - for (j = 0; j < xctrls_count; j++) {
> - if (xctrls[j].id == mapping->master_id) {
> - changes |= V4L2_EVENT_CTRL_CH_FLAGS;
> - break;
> - }
> - }
> - }
> + if (mapping->master_id &&
> + uvc_ctrl_xctrls_has_control(xctrls, xctrls_count,
> + mapping->master_id))
> + changes |= V4L2_EVENT_CTRL_CH_FLAGS;
>
> - uvc_ctrl_send_event(handle, ctrl, mapping, xctrls[i].value,
> - changes);
> + uvc_ctrl_send_event(handle->chain, handle, ctrl, mapping,
> + xctrls[i].value, changes);
> }
> }
>
> @@ -1472,9 +1573,10 @@ 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;
> @@ -1581,6 +1683,9 @@ int uvc_ctrl_set(struct uvc_video_chain *chain,
> mapping->set(mapping, value,
> uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT));
>
> + if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS)
> + ctrl->handle = handle;
> +
> ctrl->dirty = 1;
> ctrl->modified = 1;
> return 0;
> @@ -1612,7 +1717,9 @@ 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;
> @@ -2173,6 +2280,8 @@ int uvc_ctrl_init_device(struct uvc_device *dev)
> struct uvc_entity *entity;
> unsigned int i;
>
> + 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 +2350,8 @@ 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 7b71041..0722dc6 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 +103,97 @@ 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_find_ctrl(struct uvc_entity
> *entity, + u8 selector)
> {
> - char *attrs[3] = { "value", "info", "failure" };
> + 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;
> +}
>
> - if (len < 6 || data[2] != 0 || data[4] > 2) {
> +static struct uvc_control *uvc_event_find_ctrl(struct uvc_device *dev,
> + const struct uvc_control_status *status,
> + struct uvc_video_chain **chain)
> +{
> + list_for_each_entry((*chain), &dev->chains, list) {
> + struct uvc_entity *entity;
> + struct uvc_control *ctrl;
> +
> + list_for_each_entry(entity, &(*chain)->entities, chain) {
> + if (entity->id != status->bOriginator)
> + continue;
> +
> + ctrl = uvc_event_entity_find_ctrl(entity,
> + status->bSelector);
> + if (ctrl)
> + return ctrl;
> + }
> + }
> +
> + return NULL;
> +}
> +
> +static bool uvc_event_control(struct urb *urb,
> + const struct uvc_control_status *status, int len)
> +{
> + static const char *attrs[] = { "value", "info", "failure", "min", "max" };
> + struct uvc_device *dev = urb->context;
> + struct uvc_video_chain *chain;
> + struct uvc_control *ctrl;
> +
> + if (len < 6 || status->bEvent != 0 ||
> + status->bAttribute >= ARRAY_SIZE(attrs)) {
> uvc_trace(UVC_TRACE_STATUS, "Invalid control status event "
> "received.\n");
> - return;
> + return false;
> }
>
> 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 false;
> +
> + switch (status->bAttribute) {
> + case UVC_CTRL_VALUE_CHANGE:
> + return uvc_ctrl_status_event(urb, chain, ctrl, status->bValue);
> +
> + case UVC_CTRL_INFO_CHANGE:
> + case UVC_CTRL_FAILURE_CHANGE:
> + case UVC_CTRL_MIN_CHANGE:
> + case UVC_CTRL_MAX_CHANGE:
> + break;
> + }
> +
> + return false;
> }
>
> static void uvc_status_complete(struct urb *urb)
> @@ -138,13 +221,23 @@ static void uvc_status_complete(struct urb *urb)
> len = urb->actual_length;
> if (len > 0) {
> switch (dev->status[0] & 0x0f) {
> - case UVC_STATUS_TYPE_CONTROL:
> - uvc_event_control(dev, dev->status, len);
> + case UVC_STATUS_TYPE_CONTROL: {
> + struct uvc_control_status *status =
> + (struct uvc_control_status *)dev->status;
> +
> + if (uvc_event_control(urb, status, len))
> + /* The URB will be resubmitted in work context. */
> + return;
> break;
> + }
>
> - case UVC_STATUS_TYPE_STREAMING:
> - uvc_event_streaming(dev, dev->status, len);
> + case UVC_STATUS_TYPE_STREAMING: {
> + struct uvc_streaming_status *status =
> + (struct uvc_streaming_status *)dev->status;
> +
> + uvc_event_streaming(dev, status, len);
> break;
> + }
>
> default:
> uvc_trace(UVC_TRACE_STATUS, "Unknown status event "
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c
> b/drivers/media/usb/uvc/uvc_v4l2.c index bd32914..18a7384 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 be5cf17..8ae03a4 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>
> @@ -256,6 +257,8 @@ struct uvc_control {
> initialized:1;
>
> u8 *uvc_data;
> +
> + struct uvc_fh *handle; /* File handle that last changed the control. */
> };
>
> struct uvc_format_desc {
> @@ -600,6 +603,14 @@ struct uvc_device {
> u8 *status;
> struct input_dev *input;
> char input_phys[64];
> +
> + struct uvc_ctrl_work {
> + struct work_struct work;
> + struct urb *urb;
> + struct uvc_video_chain *chain;
> + struct uvc_control *ctrl;
> + const void *data;
> + } async_ctrl;
> };
>
> enum uvc_handle_state {
> @@ -753,6 +764,8 @@ 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);
> +bool uvc_ctrl_status_event(struct urb *urb, struct uvc_video_chain *chain,
> + struct uvc_control *ctrl, const u8 *data);
>
> int uvc_ctrl_begin(struct uvc_video_chain *chain);
> int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
> @@ -770,7 +783,7 @@ 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 020714d..f80f05b 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