media: v4l2-subdev: Add new ioctl for client capabilities

Add new ioctls to set and get subdev client capabilities. Client in this
context means the userspace application which opens the subdev device
node. The client capabilities are stored in the file handle of the
opened subdev device node, and the client must set the capabilities for
each opened subdev.

For now we only add a single flag, V4L2_SUBDEV_CLIENT_CAP_STREAMS, which
indicates that the client is streams-aware.

The reason for needing such a flag is as follows:

Many structs passed via ioctls, e.g. struct v4l2_subdev_format, contain
reserved fields (usually a single array field). These reserved fields
can be used to extend the ioctl. The userspace is required to zero the
reserved fields.

We recently added a new 'stream' field to many of these structs, and the
space for the field was taken from these reserved arrays. The assumption
was that these new 'stream' fields are always initialized to zero if the
userspace does not use them. This was a mistake, as, as mentioned above,
the userspace is required to zero the _reserved_ fields. In other words,
there is no requirement to zero this new stream field, and if the
userspace doesn't use the field (which is the case for all userspace
applications at the moment), the field may contain random data.

This shows that the way the reserved fields are defined in v4l2 is, in
my opinion, somewhat broken, but there is nothing to do about that.

To fix this issue we need a way for the userspace to tell the kernel
that the userspace has indeed set the 'stream' field, and it's fine for
the kernel to access it. This is achieved with the new ioctl, which the
userspace should usually use right after opening the subdev device node.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index bfb102f2121a..2ec179cd1264 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -510,8 +510,11 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	struct video_device *vdev = video_devdata(file);
 	struct v4l2_subdev *sd = vdev_to_v4l2_subdev(vdev);
 	struct v4l2_fh *vfh = file->private_data;
+	struct v4l2_subdev_fh *subdev_fh = to_v4l2_subdev_fh(vfh);
 	bool ro_subdev = test_bit(V4L2_FL_SUBDEV_RO_DEVNODE, &vdev->flags);
 	bool streams_subdev = sd->flags & V4L2_SUBDEV_FL_STREAMS;
+	bool client_supports_streams = subdev_fh->client_caps &
+				       V4L2_SUBDEV_CLIENT_CAP_STREAMS;
 	int rval;
 
 	switch (cmd) {
@@ -636,6 +639,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	case VIDIOC_SUBDEV_G_FMT: {
 		struct v4l2_subdev_format *format = arg;
 
+		if (!client_supports_streams)
+			format->stream = 0;
+
 		memset(format->reserved, 0, sizeof(format->reserved));
 		memset(format->format.reserved, 0, sizeof(format->format.reserved));
 		return v4l2_subdev_call(sd, pad, get_fmt, state, format);
@@ -647,6 +653,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 		if (format->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
 			return -EPERM;
 
+		if (!client_supports_streams)
+			format->stream = 0;
+
 		memset(format->reserved, 0, sizeof(format->reserved));
 		memset(format->format.reserved, 0, sizeof(format->format.reserved));
 		return v4l2_subdev_call(sd, pad, set_fmt, state, format);
@@ -656,6 +665,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 		struct v4l2_subdev_crop *crop = arg;
 		struct v4l2_subdev_selection sel;
 
+		if (!client_supports_streams)
+			crop->stream = 0;
+
 		memset(crop->reserved, 0, sizeof(crop->reserved));
 		memset(&sel, 0, sizeof(sel));
 		sel.which = crop->which;
@@ -677,6 +689,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 		if (crop->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
 			return -EPERM;
 
+		if (!client_supports_streams)
+			crop->stream = 0;
+
 		memset(crop->reserved, 0, sizeof(crop->reserved));
 		memset(&sel, 0, sizeof(sel));
 		sel.which = crop->which;
@@ -695,6 +710,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	case VIDIOC_SUBDEV_ENUM_MBUS_CODE: {
 		struct v4l2_subdev_mbus_code_enum *code = arg;
 
+		if (!client_supports_streams)
+			code->stream = 0;
+
 		memset(code->reserved, 0, sizeof(code->reserved));
 		return v4l2_subdev_call(sd, pad, enum_mbus_code, state,
 					code);
@@ -703,6 +721,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	case VIDIOC_SUBDEV_ENUM_FRAME_SIZE: {
 		struct v4l2_subdev_frame_size_enum *fse = arg;
 
+		if (!client_supports_streams)
+			fse->stream = 0;
+
 		memset(fse->reserved, 0, sizeof(fse->reserved));
 		return v4l2_subdev_call(sd, pad, enum_frame_size, state,
 					fse);
@@ -711,6 +732,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	case VIDIOC_SUBDEV_G_FRAME_INTERVAL: {
 		struct v4l2_subdev_frame_interval *fi = arg;
 
+		if (!client_supports_streams)
+			fi->stream = 0;
+
 		memset(fi->reserved, 0, sizeof(fi->reserved));
 		return v4l2_subdev_call(sd, video, g_frame_interval, arg);
 	}
@@ -721,6 +745,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 		if (ro_subdev)
 			return -EPERM;
 
+		if (!client_supports_streams)
+			fi->stream = 0;
+
 		memset(fi->reserved, 0, sizeof(fi->reserved));
 		return v4l2_subdev_call(sd, video, s_frame_interval, arg);
 	}
@@ -728,6 +755,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	case VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL: {
 		struct v4l2_subdev_frame_interval_enum *fie = arg;
 
+		if (!client_supports_streams)
+			fie->stream = 0;
+
 		memset(fie->reserved, 0, sizeof(fie->reserved));
 		return v4l2_subdev_call(sd, pad, enum_frame_interval, state,
 					fie);
@@ -736,6 +766,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 	case VIDIOC_SUBDEV_G_SELECTION: {
 		struct v4l2_subdev_selection *sel = arg;
 
+		if (!client_supports_streams)
+			sel->stream = 0;
+
 		memset(sel->reserved, 0, sizeof(sel->reserved));
 		return v4l2_subdev_call(
 			sd, pad, get_selection, state, sel);
@@ -747,6 +780,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 		if (sel->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
 			return -EPERM;
 
+		if (!client_supports_streams)
+			sel->stream = 0;
+
 		memset(sel->reserved, 0, sizeof(sel->reserved));
 		return v4l2_subdev_call(
 			sd, pad, set_selection, state, sel);
@@ -888,6 +924,33 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 					routing->which, &krouting);
 	}
 
+	case VIDIOC_SUBDEV_G_CLIENT_CAP: {
+		struct v4l2_subdev_client_capability *client_cap = arg;
+
+		client_cap->capabilities = subdev_fh->client_caps;
+
+		return 0;
+	}
+
+	case VIDIOC_SUBDEV_S_CLIENT_CAP: {
+		struct v4l2_subdev_client_capability *client_cap = arg;
+
+		/*
+		 * Clear V4L2_SUBDEV_CLIENT_CAP_STREAMS if streams API is not
+		 * enabled. Remove this when streams API is no longer
+		 * experimental.
+		 */
+		if (!v4l2_subdev_enable_streams_api)
+			client_cap->capabilities &= ~V4L2_SUBDEV_CLIENT_CAP_STREAMS;
+
+		/* Filter out unsupported capabilities */
+		client_cap->capabilities &= V4L2_SUBDEV_CLIENT_CAP_STREAMS;
+
+		subdev_fh->client_caps = client_cap->capabilities;
+
+		return 0;
+	}
+
 	default:
 		return v4l2_subdev_call(sd, core, ioctl, cmd, arg);
 	}