Re: [RFC PATCH] videodev2.h: introduce VIDIOC_DQEXTEVENT

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Hans,

Thanks for the patch.

On Sat, Jan 26, 2019 at 12:06:19PM +0100, Hans Verkuil wrote:
> This patch adds an extended version of VIDIOC_DQEVENT that:
> 
> 1) is Y2038 safe by using a __u64 for the timestamp
> 2) needs no compat32 conversion code
> 3) is able to handle control events from 64-bit control types
>    by changing the type of the minimum, maximum, step and default_value
>    field to __u64
> 
> All drivers and frameworks will be using this, and v4l2-ioctl.c would be the
> only place where the old event ioctl and structs are used.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
> Please let me know if there are additional requests for such a new ioctl.
> 
> Note that I am using number 104 for the ioctl, but perhaps it would be better to
> use an unused ioctl number like 1 or 3. There are quite a few holes in the
> ioctl numbers. We currently have only 82 ioctls, yet are up to ioctl number 103.
> ---
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 9a920f071ff9..969e775b8c25 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2303,6 +2303,37 @@ struct v4l2_event {
>  	__u32				reserved[8];
>  };
> 
> +struct v4l2_event_ext_ctrl {
> +	__u32 changes;
> +	__u32 type;
> +	union {
> +		__s32 value;
> +		__s64 value64;
> +	};
> +	__s64 minimum;
> +	__s64 maximum;
> +	__s64 step;
> +	__s64 default_value;
> +	__u32 flags;
> +};
> +
> +struct v4l2_ext_event {
> +	__u32				type;
> +	__u32				id;
> +	union {
> +		struct v4l2_event_vsync		vsync;
> +		struct v4l2_event_ext_ctrl	ctrl;
> +		struct v4l2_event_frame_sync	frame_sync;
> +		struct v4l2_event_src_change	src_change;
> +		struct v4l2_event_motion_det	motion_det;
> +		__u8				data[64];
> +	} u;

If I'd change something in the event IOCTL, I'd probably put the reserved
fields here. That'd allow later taking some for the use of the event data
if needed.

I might also increase the size of the event data. 64 bytes is not that
much. But you indeed end up copying it around all the time... So it's a
trade-off.

> +	__u64				timestamp;
> +	__u32				pending;
> +	__u32				sequence;
> +	__u32				reserved[8];
> +};
> +
>  #define V4L2_EVENT_SUB_FL_SEND_INITIAL		(1 << 0)
>  #define V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK	(1 << 1)
> 
> @@ -2475,6 +2506,7 @@ struct v4l2_create_buffers {
>  #define VIDIOC_DBG_G_CHIP_INFO  _IOWR('V', 102, struct v4l2_dbg_chip_info)
> 
>  #define VIDIOC_QUERY_EXT_CTRL	_IOWR('V', 103, struct v4l2_query_ext_ctrl)
> +#define	VIDIOC_DQEXTEVENT	 _IOR('V', 104, struct v4l2_ext_event)

How do you plan to name the new buffer handling IOCTLs? I.e. with or
without underscores around "EXT"?

> 
>  /* Reminder: when adding new ioctls please add support for them to
>     drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */

-- 
Kind regards,

Sakari Ailus
sakari.ailus@linux.intel.com