media: v4l: ctrls: Add debug messages

Currently, the v4l2 control code is a bit silent on errors. Add debug messages on (hopefully) most of the error paths.

Signed-off-by Ezequiel Garcia <[email protected]>

---
Changes from v1:
* Drop changes in the debug parameter semantics.
* Drop new module debug parameter.
* Add documentation.
* Add a debug error in all places where control can fail.
* Reorder the vdev parameter, to make the patch less invasive.

---
 Documentation/media/kapi/v4l2-dev.rst      |   1 +
 drivers/media/platform/omap3isp/ispvideo.c |   2 +-
 drivers/media/v4l2-core/v4l2-ctrls.c       | 106 ++++++++++++++++-----
 drivers/media/v4l2-core/v4l2-ioctl.c       |  12 +--
 drivers/media/v4l2-core/v4l2-subdev.c      |   6 +-
 include/media/v4l2-ctrls.h                 |   9 +-
 include/media/v4l2-ioctl.h                 |   2 +
 7 files changed, 100 insertions(+), 38 deletions(-)

Documentation/media/kapi/v4l2-dev.rst +1 -0

index b359f1804bbe..4c5a15c53dbf 100644
@@ -288,6 +288,7 @@ Mask  Description
 0x08  Log the read and write file operations and the VIDIOC_QBUF and
       VIDIOC_DQBUF ioctls.
 0x10  Log the poll file operation.
+0x20  Log error and messages in the control operations.
 ===== ================================================================
 
 Video device cleanup

drivers/media/platform/omap3isp/ispvideo.c +1 -1

index 175bbed9a235..abc945cc05c9 100644
@@ -1028,7 +1028,7 @@ static int isp_video_check_external_subdevs(struct isp_video *video,
 	ctrls.count = 1;
 	ctrls.controls = &ctrl;
 
-	ret = v4l2_g_ext_ctrls(pipe->external->ctrl_handler, NULL, &ctrls);
+	ret = v4l2_g_ext_ctrls(pipe->external->ctrl_handler, &video->video, NULL, &ctrls);
 	if (ret < 0) {
 		dev_warn(isp->dev, "no pixel rate control in subdev %s\n",
 			 pipe->external->name);

drivers/media/v4l2-core/v4l2-ctrls.c +2 -0

index 2d7525e2d9eb..4ee703e04ef2 100644
@@ -6,6 +6,8 @@
 
  */
 
+#define pr_fmt(fmt) "v4l2-ctrls: " fmt
+
 #include <linux/ctype.h>
 #include <linux/mm.h>
 #include <linux/slab.h>

drivers/media/v4l2-core/v4l2-ctrls.c +76 -26

+		printk(KERN_DEBUG pr_fmt("%s: %s: " fmt),		\
+		       __func__, video_device_node_name(vdev), ##arg);	\
+} while (0)
+
 #define has_op(master, op) \
 	(master->ops && master->ops->op)
 #define call_op(master, op) \

@@ -3211,6 +3219,7 @@ static int v4l2_ctrl_request_bind(struct media_request *req,
 static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
 			     struct v4l2_ext_controls *cs,
 			     struct v4l2_ctrl_helper *helpers,
+			     struct video_device *vdev,
 			     bool get)
 {
 	struct v4l2_ctrl_helper *h;

@@ -3228,20 +3237,28 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
 		if (cs->which &&
 		    cs->which != V4L2_CTRL_WHICH_DEF_VAL &&
 		    cs->which != V4L2_CTRL_WHICH_REQUEST_VAL &&
-		    V4L2_CTRL_ID2WHICH(id) != cs->which)
+		    V4L2_CTRL_ID2WHICH(id) != cs->which) {
+			dprintk(vdev, "invalid which 0x%x or control id 0x%x\n", cs->which, id);
 			return -EINVAL;
+		}
 
 		/* Old-style private controls are not allowed for
 		   extended controls */
-		if (id >= V4L2_CID_PRIVATE_BASE)
+		if (id >= V4L2_CID_PRIVATE_BASE) {
+			dprintk(vdev, "old-style private controls not allowed for extended controls\n");
 			return -EINVAL;
+		}
 		ref = find_ref_lock(hdl, id);
-		if (ref == NULL)
+		if (ref == NULL) {
+			dprintk(vdev, "cannot find control id 0x%x\n", id);
 			return -EINVAL;
+		}
 		h->ref = ref;
 		ctrl = ref->ctrl;
-		if (ctrl->flags & V4L2_CTRL_FLAG_DISABLED)
+		if (ctrl->flags & V4L2_CTRL_FLAG_DISABLED) {
+			dprintk(vdev, "control id 0x%x is disabled\n", id);
 			return -EINVAL;
+		}
 
 		if (ctrl->cluster[0]->ncontrols > 1)
 			have_clusters = true;

@@ -3251,10 +3268,16 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
 			unsigned tot_size = ctrl->elems * ctrl->elem_size;
 
 			if (c->size < tot_size) {
+				/*
+				 * In the get case the application first queries
+				 * to obtain the size of the control.
+				 */
 				if (get) {
 					c->size = tot_size;
 					return -ENOSPC;
 				}
+				dprintk(vdev, "pointer control id 0x%x size too small, %d bytes but %d bytes needed\n",
+					id, c->size, tot_size);
 				return -EFAULT;
 			}
 			c->size = tot_size;

@@ -3315,7 +3338,8 @@ static int class_check(struct v4l2_ctrl_handler *hdl, u32 which)
 
 /* Get extended controls. Allocates the helpers array if needed. */
 static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
-				   struct v4l2_ext_controls *cs)
+				   struct v4l2_ext_controls *cs,
+				   struct video_device *vdev)
 {
 	struct v4l2_ctrl_helper helper[4];
 	struct v4l2_ctrl_helper *helpers = helper;

@@ -3341,7 +3365,7 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
 			return -ENOMEM;
 	}
 
-	ret = prepare_ext_ctrls(hdl, cs, helpers, true);
+	ret = prepare_ext_ctrls(hdl, cs, helpers, vdev, true);
 	cs->error_idx = cs->count;
 
 	for (i = 0; !ret && i < cs->count; i++)

@@ -3434,8 +3458,8 @@ v4l2_ctrls_find_req_obj(struct v4l2_ctrl_handler *hdl,
 	return obj;
 }
 
-int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct media_device *mdev,
-		     struct v4l2_ext_controls *cs)
+int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct video_device *vdev,
+		     struct media_device *mdev, struct v4l2_ext_controls *cs)
 {
 	struct media_request_object *obj = NULL;
 	struct media_request *req = NULL;

@@ -3471,7 +3495,7 @@ int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct media_device *mdev,
 				   req_obj);
 	}
 
-	ret = v4l2_g_ext_ctrls_common(hdl, cs);
+	ret = v4l2_g_ext_ctrls_common(hdl, cs, vdev);
 
 	if (obj) {
 		media_request_unlock_for_access(req);

@@ -3614,7 +3638,9 @@ static int try_or_set_cluster(struct v4l2_fh *fh, struct v4l2_ctrl *master,
 
 /* Validate controls. */
 static int validate_ctrls(struct v4l2_ext_controls *cs,
-			  struct v4l2_ctrl_helper *helpers, bool set)
+			  struct v4l2_ctrl_helper *helpers,
+			  struct video_device *vdev,
+			  bool set)
 {
 	unsigned i;
 	int ret = 0;

@@ -3626,16 +3652,20 @@ static int validate_ctrls(struct v4l2_ext_controls *cs,
 
 		cs->error_idx = i;
 
-		if (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY)
+		if (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY) {
+			dprintk(vdev, "control id 0x%x is read-only\n", ctrl->id);
 			return -EACCES;
+		}
 		/* This test is also done in try_set_control_cluster() which
 		   is called in atomic context, so that has the final say,
 		   but it makes sense to do an up-front check as well. Once
 		   an error occurs in try_set_control_cluster() some other
 		   controls may have been set already and we want to do a
 		   best-effort to avoid that. */
-		if (set && (ctrl->flags & V4L2_CTRL_FLAG_GRABBED))
+		if (set && (ctrl->flags & V4L2_CTRL_FLAG_GRABBED)) {
+			dprintk(vdev, "control id 0x%x is grabbed, cannot set\n", ctrl->id);
 			return -EBUSY;
+		}
 		/*
 		 * Skip validation for now if the payload needs to be copied
 		 * from userspace into kernelspace. We'll validate those later.

@@ -3670,7 +3700,8 @@ static void update_from_auto_cluster(struct v4l2_ctrl *master)
 /* Try or try-and-set controls */
 static int try_set_ext_ctrls_common(struct v4l2_fh *fh,
 				    struct v4l2_ctrl_handler *hdl,
-				    struct v4l2_ext_controls *cs, bool set)
+				    struct v4l2_ext_controls *cs,
+				    struct video_device *vdev, bool set)
 {
 	struct v4l2_ctrl_helper helper[4];
 	struct v4l2_ctrl_helper *helpers = helper;

@@ -3680,13 +3711,17 @@ static int try_set_ext_ctrls_common(struct v4l2_fh *fh,
 	cs->error_idx = cs->count;
 
 	/* Default value cannot be changed */
-	if (cs->which == V4L2_CTRL_WHICH_DEF_VAL)
+	if (cs->which == V4L2_CTRL_WHICH_DEF_VAL) {
+		dprintk(vdev, "%s: cannot change default value\n", video_device_node_name(vdev));
 		return -EINVAL;
+	}
 
 	cs->which = V4L2_CTRL_ID2WHICH(cs->which);
 
-	if (hdl == NULL)
+	if (hdl == NULL) {
+		dprintk(vdev, "%s: invalid null control handler\n", video_device_node_name(vdev));
 		return -EINVAL;
+	}
 
 	if (cs->count == 0)
 		return class_check(hdl, cs->which);

@@ -3697,9 +3732,9 @@ static int try_set_ext_ctrls_common(struct v4l2_fh *fh,
 		if (!helpers)
 			return -ENOMEM;
 	}
-	ret = prepare_ext_ctrls(hdl, cs, helpers, false);
+	ret = prepare_ext_ctrls(hdl, cs, helpers, vdev, false);
 	if (!ret)
-		ret = validate_ctrls(cs, helpers, set);
+		ret = validate_ctrls(cs, helpers, vdev, set);
 	if (ret && set)
 		cs->error_idx = cs->count;
 	for (i = 0; !ret && i < cs->count; i++) {

@@ -3784,7 +3819,8 @@ static int try_set_ext_ctrls_common(struct v4l2_fh *fh,
 }
 
 static int try_set_ext_ctrls(struct v4l2_fh *fh,
-			     struct v4l2_ctrl_handler *hdl, struct media_device *mdev,
+			     struct v4l2_ctrl_handler *hdl,
+			     struct video_device *vdev, struct media_device *mdev,
 			     struct v4l2_ext_controls *cs, bool set)
 {
 	struct media_request_object *obj = NULL;

@@ -3792,21 +3828,32 @@ static int try_set_ext_ctrls(struct v4l2_fh *fh,
 	int ret;
 
 	if (cs->which == V4L2_CTRL_WHICH_REQUEST_VAL) {
-		if (!mdev || cs->request_fd < 0)
+		if (!mdev) {
+			dprintk(vdev, "%s: missing media device\n", video_device_node_name(vdev));
+			return -EINVAL;
+		}
+
+		if (cs->request_fd < 0) {
+			dprintk(vdev, "%s: invalid request fd %d\n", video_device_node_name(vdev), cs->request_fd);
 			return -EINVAL;
+		}
 
 		req = media_request_get_by_fd(mdev, cs->request_fd);
-		if (IS_ERR(req))
+		if (IS_ERR(req)) {
+			dprintk(vdev, "%s: cannot find request fd %d\n", video_device_node_name(vdev), cs->request_fd);
 			return PTR_ERR(req);
+		}
 
 		ret = media_request_lock_for_update(req);
 		if (ret) {
+			dprintk(vdev, "%s: cannot lock request fd %d\n", video_device_node_name(vdev), cs->request_fd);
 			media_request_put(req);
 			return ret;
 		}
 
 		obj = v4l2_ctrls_find_req_obj(hdl, req, set);
 		if (IS_ERR(obj)) {
+			dprintk(vdev, "%s: cannot find request object for request fd %d\n", video_device_node_name(vdev), cs->request_fd);
 			media_request_unlock_for_update(req);
 			media_request_put(req);
 			return PTR_ERR(obj);

@@ -3815,7 +3862,9 @@ static int try_set_ext_ctrls(struct v4l2_fh *fh,
 				   req_obj);
 	}
 
-	ret = try_set_ext_ctrls_common(fh, hdl, cs, set);
+	ret = try_set_ext_ctrls_common(fh, hdl, cs, vdev, set);
+	if (ret)
+		dprintk(vdev, "%s: try_set_ext_ctrls_common failed (%d)\n", video_device_node_name(vdev), ret);
 
 	if (obj) {
 		media_request_unlock_for_update(req);

@@ -3826,17 +3875,22 @@ static int try_set_ext_ctrls(struct v4l2_fh *fh,
 	return ret;
 }
 
-int v4l2_try_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct media_device *mdev,
+int v4l2_try_ext_ctrls(struct v4l2_ctrl_handler *hdl,
+		       struct video_device *vdev,
+		       struct media_device *mdev,
 		       struct v4l2_ext_controls *cs)
 {
-	return try_set_ext_ctrls(NULL, hdl, mdev, cs, false);
+	return try_set_ext_ctrls(NULL, hdl, vdev, mdev, cs, false);
 }
 EXPORT_SYMBOL(v4l2_try_ext_ctrls);
 
-int v4l2_s_ext_ctrls(struct v4l2_fh *fh, struct v4l2_ctrl_handler *hdl,
-		     struct media_device *mdev, struct v4l2_ext_controls *cs)
+int v4l2_s_ext_ctrls(struct v4l2_fh *fh,
+		     struct v4l2_ctrl_handler *hdl,
+		     struct video_device *vdev,
+		     struct media_device *mdev,
+		     struct v4l2_ext_controls *cs)
 {
-	return try_set_ext_ctrls(fh, hdl, mdev, cs, true);
+	return try_set_ext_ctrls(fh, hdl, vdev, mdev, cs, true);
 }
 EXPORT_SYMBOL(v4l2_s_ext_ctrls);
 

drivers/media/v4l2-core/v4l2-ioctl.c +6 -6

index b1f4b991dba6..e95efea1a9ca 100644
@@ -2165,9 +2165,9 @@ static int v4l_g_ext_ctrls(const struct v4l2_ioctl_ops *ops,
 
 	p->error_idx = p->count;
 	if (vfh && vfh->ctrl_handler)
-		return v4l2_g_ext_ctrls(vfh->ctrl_handler, vfd->v4l2_dev->mdev, p);
+		return v4l2_g_ext_ctrls(vfh->ctrl_handler, vfd, vfd->v4l2_dev->mdev, p);
 	if (vfd->ctrl_handler)
-		return v4l2_g_ext_ctrls(vfd->ctrl_handler, vfd->v4l2_dev->mdev, p);
+		return v4l2_g_ext_ctrls(vfd->ctrl_handler, vfd, vfd->v4l2_dev->mdev, p);
 	if (ops->vidioc_g_ext_ctrls == NULL)
 		return -ENOTTY;
 	return check_ext_ctrls(p, 0) ? ops->vidioc_g_ext_ctrls(file, fh, p) :

@@ -2184,9 +2184,9 @@ static int v4l_s_ext_ctrls(const struct v4l2_ioctl_ops *ops,
 
 	p->error_idx = p->count;
 	if (vfh && vfh->ctrl_handler)
-		return v4l2_s_ext_ctrls(vfh, vfh->ctrl_handler, vfd->v4l2_dev->mdev, p);
+		return v4l2_s_ext_ctrls(vfh, vfh->ctrl_handler, vfd, vfd->v4l2_dev->mdev, p);
 	if (vfd->ctrl_handler)
-		return v4l2_s_ext_ctrls(NULL, vfd->ctrl_handler, vfd->v4l2_dev->mdev, p);
+		return v4l2_s_ext_ctrls(NULL, vfd->ctrl_handler, vfd, vfd->v4l2_dev->mdev, p);
 	if (ops->vidioc_s_ext_ctrls == NULL)
 		return -ENOTTY;
 	return check_ext_ctrls(p, 0) ? ops->vidioc_s_ext_ctrls(file, fh, p) :

@@ -2203,9 +2203,9 @@ static int v4l_try_ext_ctrls(const struct v4l2_ioctl_ops *ops,
 
 	p->error_idx = p->count;
 	if (vfh && vfh->ctrl_handler)
-		return v4l2_try_ext_ctrls(vfh->ctrl_handler, vfd->v4l2_dev->mdev, p);
+		return v4l2_try_ext_ctrls(vfh->ctrl_handler, vfd, vfd->v4l2_dev->mdev, p);
 	if (vfd->ctrl_handler)
-		return v4l2_try_ext_ctrls(vfd->ctrl_handler, vfd->v4l2_dev->mdev, p);
+		return v4l2_try_ext_ctrls(vfd->ctrl_handler, vfd, vfd->v4l2_dev->mdev, p);
 	if (ops->vidioc_try_ext_ctrls == NULL)
 		return -ENOTTY;
 	return check_ext_ctrls(p, 0) ? ops->vidioc_try_ext_ctrls(file, fh, p) :

drivers/media/v4l2-core/v4l2-subdev.c +3 -3

index f24978b80440..1b5edd3b1e6c 100644
@@ -211,19 +211,19 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 		if (!vfh->ctrl_handler)
 			return -ENOTTY;
 		return v4l2_g_ext_ctrls(vfh->ctrl_handler,
-					sd->v4l2_dev->mdev, arg);
+					vdev, sd->v4l2_dev->mdev, arg);
 
 	case VIDIOC_S_EXT_CTRLS:
 		if (!vfh->ctrl_handler)
 			return -ENOTTY;
 		return v4l2_s_ext_ctrls(vfh, vfh->ctrl_handler,
-					sd->v4l2_dev->mdev, arg);
+					vdev, sd->v4l2_dev->mdev, arg);
 
 	case VIDIOC_TRY_EXT_CTRLS:
 		if (!vfh->ctrl_handler)
 			return -ENOTTY;
 		return v4l2_try_ext_ctrls(vfh->ctrl_handler,
-					  sd->v4l2_dev->mdev, arg);
+					  vdev, sd->v4l2_dev->mdev, arg);
 
 	case VIDIOC_DQEVENT:
 		if (!(sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS))

include/media/v4l2-ctrls.h +7 -2

index b4433483af23..c08d6cc56743 100644
@@ -1265,25 +1265,28 @@ int v4l2_s_ctrl(struct v4l2_fh *fh, struct v4l2_ctrl_handler *hdl,
  *	:ref:`VIDIOC_G_EXT_CTRLS <vidioc_g_ext_ctrls>` ioctl
  *
  * @hdl: pointer to &struct v4l2_ctrl_handler
+ * @vdev: pointer to &struct video_device
  * @mdev: pointer to &struct media_device
  * @c: pointer to &struct v4l2_ext_controls
  *
  * If hdl == NULL then they will all return -EINVAL.
  */
-int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct media_device *mdev,
-		     struct v4l2_ext_controls *c);
+int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct video_device *vdev,
+		     struct media_device *mdev, struct v4l2_ext_controls *c);
 
 /**
  * v4l2_try_ext_ctrls - Helper function to implement
  *	:ref:`VIDIOC_TRY_EXT_CTRLS <vidioc_g_ext_ctrls>` ioctl
  *
  * @hdl: pointer to &struct v4l2_ctrl_handler
+ * @vdev: pointer to &struct video_device
  * @mdev: pointer to &struct media_device
  * @c: pointer to &struct v4l2_ext_controls
  *
  * If hdl == NULL then they will all return -EINVAL.
  */
 int v4l2_try_ext_ctrls(struct v4l2_ctrl_handler *hdl,
+		       struct video_device *vdev,
 		       struct media_device *mdev,
 		       struct v4l2_ext_controls *c);
 

@@ -1293,12 +1296,14 @@ int v4l2_try_ext_ctrls(struct v4l2_ctrl_handler *hdl,
  *
  * @fh: pointer to &struct v4l2_fh
  * @hdl: pointer to &struct v4l2_ctrl_handler
+ * @vdev: pointer to &struct video_device
  * @mdev: pointer to &struct media_device
  * @c: pointer to &struct v4l2_ext_controls
  *
  * If hdl == NULL then they will all return -EINVAL.
  */
 int v4l2_s_ext_ctrls(struct v4l2_fh *fh, struct v4l2_ctrl_handler *hdl,
+		     struct video_device *vdev,
 		     struct media_device *mdev,
 		     struct v4l2_ext_controls *c);
 

include/media/v4l2-ioctl.h +2 -0

index 400f2e46c108..4bba65a59d46 100644
@@ -602,6 +602,8 @@ struct v4l2_ioctl_ops {
 #define V4L2_DEV_DEBUG_STREAMING	0x08
 /* Log poll() */
 #define V4L2_DEV_DEBUG_POLL		0x10
+/* Log controls */
+#define V4L2_DEV_DEBUG_CTRL		0x20
 
 /*  Video standard functions  */
 

Quoted 60 lines · Ezequiel Garcia

Currently, the v4l2 control code is a bit silent on errors. Add debug messages on (hopefully) most of the error paths.

Signed-off-by Ezequiel Garcia <[email protected]>

---
Changes from v1:
* Drop changes in the debug parameter semantics.
* Drop new module debug parameter.
* Add documentation.
* Add a debug error in all places where control can fail.
* Reorder the vdev parameter, to make the patch less invasive.

---
 Documentation/media/kapi/v4l2-dev.rst      |   1 +
 drivers/media/platform/omap3isp/ispvideo.c |   2 +-
 drivers/media/v4l2-core/v4l2-ctrls.c       | 106 ++++++++++++++++-----
 drivers/media/v4l2-core/v4l2-ioctl.c       |  12 +--
 drivers/media/v4l2-core/v4l2-subdev.c      |   6 +-
 include/media/v4l2-ctrls.h                 |   9 +-
 include/media/v4l2-ioctl.h                 |   2 +
 7 files changed, 100 insertions(+), 38 deletions(-)

Documentation/media/kapi/v4l2-dev.rst +1 -0

index b359f1804bbe..4c5a15c53dbf 100644
@@ -288,6 +288,7 @@ Mask  Description
 0x08  Log the read and write file operations and the VIDIOC_QBUF and
       VIDIOC_DQBUF ioctls.
 0x10  Log the poll file operation.
+0x20  Log error and messages in the control operations.
 ===== ================================================================
 
 Video device cleanup

drivers/media/platform/omap3isp/ispvideo.c +1 -1

index 175bbed9a235..abc945cc05c9 100644
@@ -1028,7 +1028,7 @@ static int isp_video_check_external_subdevs(struct isp_video *video,
 	ctrls.count = 1;
 	ctrls.controls = &ctrl;
 
-	ret = v4l2_g_ext_ctrls(pipe->external->ctrl_handler, NULL, &ctrls);
+	ret = v4l2_g_ext_ctrls(pipe->external->ctrl_handler, &video->video, NULL, &ctrls);
 	if (ret < 0) {
 		dev_warn(isp->dev, "no pixel rate control in subdev %s\n",
 			 pipe->external->name);

drivers/media/v4l2-core/v4l2-ctrls.c +2 -0

index 2d7525e2d9eb..4ee703e04ef2 100644
@@ -6,6 +6,8 @@
 
  */
 
+#define pr_fmt(fmt) "v4l2-ctrls: " fmt
+
 #include <linux/ctype.h>
 #include <linux/mm.h>
 #include <linux/slab.h>

drivers/media/v4l2-core/v4l2-ctrls.c line 22

Quoted 5 lines

drivers/media/v4l2-core/v4l2-ctrls.c +2 -0

@@ -16,6 +18,12 @@
 #include <media/v4l2-event.h>
 #include <media/v4l2-dev.h>
 
+#define dprintk(vdev, fmt, arg...) do {					\
+	if (vdev->dev_debug & V4L2_DEV_DEBUG_CTRL)			\

This isn't very robust if vdev is NULL. I know it shouldn't, but it's better to check for this.

I'd use this instead:

	if (!WARN_ON(!vdev) && ((vdev)->dev_debug & V4L2_DEV_DEBUG_CTRL))			\

That way nothing crashes if vdev is NULL, and you get a warning as well in that case.