Re: [RFCv1 PATCH 1/6] videodev2.h: add enum/query/cap dv_timings ioctls.

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 03-02-2012 08:06, Hans Verkuil escreveu:
> From: Hans Verkuil <hans.verkuil@cisco.com>
> 
> These new ioctls make it possible for the dv_timings API to replace
> the dv_preset API eventually.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> ---
>  include/linux/videodev2.h |  110 ++++++++++++++++++++++++++++++++++++++++----
>  1 files changed, 100 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> index 0db0503..e59cd02 100644
> --- a/include/linux/videodev2.h
> +++ b/include/linux/videodev2.h
> @@ -987,28 +987,42 @@ struct v4l2_dv_enum_preset {
>   */
>  
>  /* BT.656/BT.1120 timing data */
> +
> +/*
> + * A note regarding vertical interlaced timings: height refers to the total
> + * height of the frame (= two fields). The blanking timings refer
> + * to the blanking of each field. So the height of the active frame is
> + * calculated as follows:
> + *
> + * act_height = height - vfrontporch - vsync - vbackporch -
> + *                       il_vfrontporch - il_vsync - il_vbackporch
> + *
> + * The active height of each field is act_height / 2.
> + */
>  struct v4l2_bt_timings {
> -	__u32	width;		/* width in pixels */
> -	__u32	height;		/* height in lines */
> +	__u32	width;		/* total frame width in pixels */
> +	__u32	height;		/* total frame height in lines */
>  	__u32	interlaced;	/* Interlaced or progressive */
>  	__u32	polarities;	/* Positive or negative polarity */
>  	__u64	pixelclock;	/* Pixel clock in HZ. Ex. 74.25MHz->74250000 */
> -	__u32	hfrontporch;	/* Horizpontal front porch in pixels */
> +	__u32	hfrontporch;	/* Horizontal front porch in pixels */
>  	__u32	hsync;		/* Horizontal Sync length in pixels */
>  	__u32	hbackporch;	/* Horizontal back porch in pixels */
>  	__u32	vfrontporch;	/* Vertical front porch in pixels */
>  	__u32	vsync;		/* Vertical Sync length in lines */
>  	__u32	vbackporch;	/* Vertical back porch in lines */
> -	__u32	il_vfrontporch;	/* Vertical front porch for bottom field of
> -				 * interlaced field formats
> +	__u32	il_vfrontporch;	/* Vertical front porch for the even field
> +				 * (aka field 2) of interlaced field formats
>  				 */
> -	__u32	il_vsync;	/* Vertical sync length for bottom field of
> -				 * interlaced field formats
> +	__u32	il_vsync;	/* Vertical sync length for the even field
> +				 * (aka field 2) of interlaced field formats
>  				 */
> -	__u32	il_vbackporch;	/* Vertical back porch for bottom field of
> -				 * interlaced field formats
> +	__u32	il_vbackporch;	/* Vertical back porch for the even field
> +				 * (aka field 2) of interlaced field formats
>  				 */
> -	__u32	reserved[16];
> +	__u32	standards;	/* Standards the timing belongs to */
> +	__u32	flags;		/* Flags */
> +	__u32	reserved[14];
>  } __attribute__ ((packed));
>  
>  /* Interlaced or progressive format */
> @@ -1019,6 +1033,37 @@ struct v4l2_bt_timings {
>  #define V4L2_DV_VSYNC_POS_POL	0x00000001
>  #define V4L2_DV_HSYNC_POS_POL	0x00000002
>  
> +/* Timings standards */
> +#define V4L2_DV_BT_STD_CEA861	(1 << 0)  /* CEA-861 Digital TV Profile */
> +#define V4L2_DV_BT_STD_DMT	(1 << 1)  /* VESA Discrete Monitor Timings */
> +#define V4L2_DV_BT_STD_CVT	(1 << 2)  /* VESA Coordinated Video Timings */
> +#define V4L2_DV_BT_STD_GTF	(1 << 3)  /* VESA Generalized Timings Formula */
> +
> +/* Flags */
> +
> +/* CVT/GTF specific: timing uses reduced blanking (CVT) or the 'Secondary
> +   GTF' curve (GTF). In both cases the horizontal and/or vertical blanking
> +   intervals are reduced, allowing a higher resolution over the same
> +   bandwidth. This is a read-only flag. */
> +#define V4L2_DV_FL_REDUCED_BLANKING		(1 << 0)

> +/* CEA-861 specific: set for CEA-861 formats with a framerate of a multiple
> +   of six. These formats can be optionally played at 1 / 1.001 speed to
> +   be compatible with the normal NTSC framerate of 29.97 frames per second.
> +   This is a read-only flag. */
> +#define V4L2_DV_FL_NTSC_COMPATIBLE		(1 << 1)
> +/* CEA-861 specific: only valid for video transmitters, the flag is cleared
> +   by receivers.
> +   If the framerate of the format is a multiple of six, then the pixelclock
> +   used to set up the transmitter is divided by 1.001 to make it compatible
> +   with NTSC framerates. Otherwise this flag is cleared. If the transmitter
> +   can't generate such frequencies, then the flag will also be cleared. */
> +#define V4L2_DV_FL_DIVIDE_CLOCK_BY_1_001	(1 << 2)

The two above have a conceptual problem: NTSC has nothing to do with the frequency.

While, in practice, NTSC is only used on Countries with 60Hz power supply, and a
1000/1001 shift is used there, to avoid flicker with the light bulbs, the 
standard doesn't mean a 29.97 Hz frame rate. 

If you take a look at CEA-861, it doesn't mention there NTSC (well, except for a 
reference for the existing standards), to avoid such conceptual issue.

Besides that,  PAL/M (and PAL/60) also uses a 29.97 Hz frame rate, in order to avoid 
flicker.

So, please don't call the flag as "NTSC_COMPATIBLE", and please fix the comments
to either not mention NTSC, or to use something more generic, like replacing:

	"...be compatible with the normal NTSC framerateof 29.97 frames per second."
with
	"...be compatible with 60Hz based standards that use a framerate of 29.97
	 frames per second, like NTSC and PAL/M."

> +/* Specific to interlaced formats: if set, then field 1 is really one half-line
> +   longer and field 2 is really one half-line shorter, so each field has
> +   exactly the same number of half-lines. Whether half-lines can be detected
> +   or used depends on the hardware. */
> +#define V4L2_DV_FL_HALF_LINE			(1 << 0)
> +
>  
>  /* DV timings */
>  struct v4l2_dv_timings {
> @@ -1032,6 +1077,47 @@ struct v4l2_dv_timings {
>  /* Values for the type field */
>  #define V4L2_DV_BT_656_1120	0	/* BT.656/1120 timing type */
>  
> +
> +/* DV timings enumeration */
> +struct v4l2_enum_dv_timings {
> +	__u32 index;
> +	__u32 reserved[3];
> +	struct v4l2_dv_timings timings;
> +};
> +
> +/* BT.656/BT.1120 timing capabilities */
> +struct v4l2_bt_timings_cap {
> +	__u32	min_width;	/* width in pixels */
> +	__u32	max_width;	/* width in pixels */
> +	__u32	min_height;	/* height in lines */
> +	__u32	max_height;	/* height in lines */
> +	__u64	min_pixelclock;	/* Pixel clock in HZ. Ex. 74.25MHz->74250000 */
> +	__u64	max_pixelclock;	/* Pixel clock in HZ. Ex. 74.25MHz->74250000 */
> +	__u32	standards;	/* Supported standards */
> +	__u32	capabilities;	/* See below */
> +	__u32	reserved[16];
> +} __attribute__ ((packed));

Hmm... why to define a new struct here, instead of just use struct v4l2_bt_timings ?

> +
> +/* Supports interlaced formats */
> +#define V4L2_DV_BT_CAP_INTERLACED	(1 << 0)
> +/* Supports progressive formats */
> +#define V4L2_DV_BT_CAP_PROGRESSIVE	(1 << 1)
> +/* Supports CVT/GTF reduced blanking */
> +#define V4L2_DV_BT_CAP_REDUCED_BLANKING	(1 << 2)
> +/* Supports custom formats */
> +#define V4L2_DV_BT_CAP_CUSTOM		(1 << 3)
> +
> +/* DV timings capabilities */
> +struct v4l2_dv_timings_cap {
> +	__u32 type;

What are the posible values for type?

Btw, it is a good idea to use kernel-doc-nano to describe the structures:

/**
 * struct v4l2_dv_timings_cap - DV timings capabilities
 * @type:	some description
...
 */

As it documents better what is defined there.

> +	__u32 reserved[3];
> +	union {
> +		struct v4l2_bt_timings_cap bt;
> +		__u32 raw_data[32];
> +	};
> +};
> +
> +
>  /*
>   *	V I D E O   I N P U T S
>   */
> @@ -2318,6 +2404,10 @@ struct v4l2_create_buffers {
>  #define VIDIOC_G_SELECTION	_IOWR('V', 94, struct v4l2_selection)
>  #define VIDIOC_S_SELECTION	_IOWR('V', 95, struct v4l2_selection)
>  
> +#define VIDIOC_ENUM_DV_TIMINGS  _IOWR('V', 96, struct v4l2_enum_dv_timings)
> +#define VIDIOC_QUERY_DV_TIMINGS  _IOR('V', 97, struct v4l2_dv_timings)
> +#define VIDIOC_DV_TIMINGS_CAP   _IOWR('V', 98, struct v4l2_dv_timings_cap)
> +
>  /* Reminder: when adding new ioctls please add support for them to
>     drivers/media/video/v4l2-compat-ioctl32.c as well! */
>