Hi Murali,
Thanks for your work on this!
See below for a few notes I made.
On Monday 14 September 2009 15:51:28 Karicheri, Muralidharan wrote:
> RFC: V4L - Support for video timings at the input/output interface
>
> Thanks to Hans Verkuil for his initial proposal and feedbacks to help write
> this RFC.
>
> Version : 1.0
>
> Background
> -----------
>
> Currently v4l2 specification supports capturing video frames from TV signals
> using tuners (input type V4L2_INPUT_TYPE_TUNER) and baseband TV signals
> (V4L2_INPUT_TYPE_CAMERA) and sensors. Similarly on the output side, the
> signals could be TV signal (V4L2_OUTPUT_TYPE_MODULATOR), baseband TV signal
> (V4L2_OUTPUT_TYPE_ANALOG) or hybrid analog VGA overlay
> (V4L2_OUTPUT_TYPE_ANALOGVGAOVERLAY) which output from a graphics card and
> then use chromakeying to replace part of the picture with the video.
> V4L2_OUTPUT_TYPE_ANALOG & V4L2_INPUT_TYPE_CAMERA are for analog interfaces
> that includes composite, S-Video and VGA (for output only). Note that even
> though VGA is a supported output, we don't have anyway to set the standard or
> timing on the output. Standard ids are only defined for TVs using
> v4l2_std_id and a set of bit masks defined for analog TV standards.
>
> Today we have a wide variety of different interfaces available to
> transmit/receive video or graphics content between source device and
> destination device. Following are some of the interfaces used in addition to
> the ones described in the v4l2 specification.
>
> Component analog input/output interface - ED/HD video
> DVI - Digital only, ANALOG only, DVI integrated that support Digital and
> Analog; Dual Link - Where second data link is used for higher
> bandwidth
> SDI - Serial digital interface standardized by SMPTE
> HDMI - HD video and Audio
> DisplayPort - digital audio/video interconnect by VESA
>
> V4L2 specification currently defined NTSC/PAL/SECAM (all variants) standards
> for describing the timing of the signal transmitted over these interfaces.
> Even though the specification defined ANALOG output type for VGA, there are
> no ways to set the timings used for output to VGA or LCD display monitors.
> Some of the proprietary implementations used existing standards IOCTL,
> VIDIOC_S_STD, to set these timings over these interfaces.
> For example, TI has Video Processing Back End (VPBE) on various media SOCs
> (Eg, DM6446, DM355 etc) that can output signal for Analog TV and VGA
> interfaces (using Digital LCD port) and support timing for displaying SD and
> HD videos (1080i, 1080p and 720p) as well as over VGA interface to a CRT or
> LCD display monitor. So we need to enhance the v4l2 specification to allow
> applications to set these timings in the capture or output devices. This RFC
> proposes to add new IOCTLs for setting/getting timings over the different
> interfaces described above and freeze the the use of existing standards
> IOCTL and standards IDs for analog TVs only.
>
> Timings
> -------
>
> The timing at the analog or digital interface that are not covered by the
> v4l2_std_id can be defined using a set of preset timings that are used by the
> hardware where these timings are predefined or by a set of timing values
> which can be configured at the hardware to generate the signal expected at
> the interface. The former will be used for hardware like TVP7002/THS8200
> which specifies preset timing required for output HD video such 1080i50/60,
> 720p50/60 etc. The latter can be used for hardware that require configuration
> of frame timing such as front porch, hsync length, vsync length, pixel clock
> etc. For example the earlier mentioned TI SOCs has a Digital LCD port that
> can be configured to output different timing values expected by LCD Display
> monitors.
>
> Preset timings (defined by VESA, SMPTE or BT.656/BT.1120 or others) can be
> defined by the following structure:-
>
> struct v4l2_dv_preset {
> __u32 preset;
> __u32 reserved[4];
> };
>
> Where preset is one of the following values:-
>
> #define V4L2_DV_CUSTOM 0x00000000
> #define V4L2_DV_480I59_94 0x00000001
> #define V4L2_DV_480I60 0x00000002
> #define V4L2_DV_480P23_976 0x00000003
> #define V4L2_DV_480P24 0x00000004
> #define V4L2_DV_480P29_97 0x00000005
> #define V4L2_DV_480P30 0x00000006
> #define V4L2_DV_576I50 0x00000007
> #define V4L2_DV_576P25 0x00000008
> #define V4L2_DV_576P50 0x00000009
> #define V4L2_DV_720P23_976 0x0000000A
> #define V4L2_DV_720P24 0x0000000B
> #define V4L2_DV_720P25 0x0000000C
> #define V4L2_DV_720P29_97 0x0000000C
> #define V4L2_DV_720P30 0x0000000D
> #define V4L2_DV_720P50 0x0000000E
> #define V4L2_DV_720P59_94 0x0000000F
> #define V4L2_DV_720P60 0x00000010
> #define V4L2_DV_1080I50 0x00000011
> #define V4L2_DV_1080I59_94 0x00000012
> #define V4L2_DV_1080I60 0x00000013
> #define V4L2_DV_1080P23_976 0x00000014
> #define V4L2_DV_1080P24 0x00000015
> #define V4L2_DV_1080P25 0x00000016
> #define V4L2_DV_1080P29_97 0x00000017
> #define V4L2_DV_1080P30 0x00000018
> #define V4L2_DV_1080P60 0x00000019
>
>
> /* Following preset value is used by driver to indicate there is no signal
> detected or could not lock to the signal for VIDIOC_QUERY_DV_PRESET.
> */
> #define V4L2_DV_INVALID 0xFFFFFFFF
>
>
> This list is expected grow over time. So a bit mask is not used for this
> (Unlike analog TV standards) so that many presets can be defined as needed in
> the future.
>
> To enumerate the DV preset timings available, applications call
> VIDIOC_ENUM_DV_PRESETS
> using the following structure:-
>
> struct v4l2_dv_enum_presets {
> __u32 index;
> __u32 preset;
> __u8 name[32]; /* Name of the preset timing */
> __u32 reserved[4];
> };
>
> Application set/get the preset by calling VIDIOC_S/G_DV_PRESET using
> v4l2_dv_preset structure.
>
> Also add a capabilities field in the input and output structure to support
> presets
>
> /*
> * V I D E O I N P U T S
> */
> struct v4l2_input {
> __u32 index; /* Which input */
> __u8 name[32]; /* Label */
> __u32 type; /* Type of input */
> __u32 audioset; /* Associated audios (bitfield) */
> __u32 tuner; /* Associated tuner */
> v4l2_std_id std;
> __u32 status;
> __u32 capabilities;
> __u32 reserved[3];
> };
>
> /*
> * V I D E O O U T P U T S
> */
> struct v4l2_output {
> __u32 index; /* Which output */
> __u8 name[32]; /* Label */
> __u32 type; /* Type of output */
> __u32 audioset; /* Associated audios (bitfield) */
> __u32 modulator; /* Associated modulator */
> v4l2_std_id std;
> __u32 capabilities;
> __u32 reserved[3];
> };
>
> where capabilities are:-
>
> #define V4L2_SUPPORTS_PRESETS 0x00000001
> #define V4L2_SUPPORTS_CUSTOM_TIMINGS 0x00000002
Rather than use 'SUPPORTS' we should rename it as 'IO_CAP'. That's more in
line with the existing naming conventions.
I also suggest adding V4L2_IO_CAP_STD if the regular S_STD is supported.
This will require going through the code and adding it, although we can
probably also set these caps in v4l2-ioctl automatically.
>
> For setting custom timing at the device, following structure is used which
> defines the complete set of timing values required at the input and output
> interface:-
>
> /* timing data values specified by various standards such as BT.1120, BT.656
> etc. */
>
> /* bt.656/bt.1120 timing data */
> struct v4l2_bt_timings {
> __u32 interlaced;
> __u64 pixelclock;
> __u32 width, height;
> __u32 polarities;
> __u32 hfrontporch, hsync, htotal;
> __u32 vfrontporch, vsync, vtotal;
> /* timings for bottom frame for interlaced formats */
> __u32 il_vtotal;
> __u32 reserved[16];
> };
>
>
> interlaced - Interlaced or progressive. use following values:-
>
> #define V4L2_DV_INTERLACED 0
> #define V4L2_DV_PROGRESSIVE 1
>
> pixelclock - expressed in HZ. So for 74.25MHz, use 74250000.
> width - number of pixels in horizontal direction
> height - number of lines in vertical direction
> polarities - Bit mask for following polarities to begin with
>
> #define V4L2_DV_VSYNC_POS_POL 0x1
> #define V4L2_DV_VSYNC_NEG_POL 0x2
> #define V4L2_DV_HSYNC_POS_POL 0x3
> #define V4L2_DV_HSYNC_NEG_POL 0x4
Why have separate pos and neg bits? Also, bitmask defines should define the
actual mask, not the bit numbers.
>
> hfrontporch,hsync, and htotal for horizontal direction and vfrontporch,vsync,
> and vtotal for vertical direction. il_vtotal is the number of vertical lines
> for interlaced video for bottom field.
>
> To define a particular timing type, following enum is used:-
>
> enum v4l2_dv_timings_type {
> V4L2_DV_BT_656_1120,
> };
>
> This will allow adding new timing types in the future.
>
> If the driver supports a set of custom timing, it can be set/get using
> VIDIOC_S/G_DV_TIMINGS
> IOCTL and specifying timings using the structure
>
> struct v4l2_dv_timings {
> enum v4l2_dv_timings_type type;
> union {
> struct v4l2_bt_timings bt;
> __u32 reserved[32];
> };
> };
>
>
> If the driver supports custom timing as well as Presets, it will return
> V4L2_DV_CUSTOM along with other preset timings for the VIDIOC_ENUM_DV_PRESETS
> IOCTL call. Application can then call VIDIOC_S/G_TIMING to get/set custom
> timings at the driver.
>
> To detect a preset timing at the input application calls
> VIDIOC_QUERY_DV_PRESET which returns the preset using the v4l2_dv_preset
> structure.
>
> Summary of new ioctls added by this RFC.
>
> #define VIDIOC_ENUM_DV_PRESETS _IOWR('V', 79, struct v4l2_dv_enum_presets)
> #define VIDIOC_S_DV_PRESET _IOWR('V', 80, struct v4l2_dv_preset)
> #define VIDIOC_G_DV_PRESET _IOWR('V', 81, struct v4l2_dv_preset)
> #define VIDIOC_QUERY_DV_PRESET _IOR('V', 82, struct v4l2_dv_preset)
> #define VIDIOC_S_DV_TIMINGS _IOWR('V', 83, struct v4l2_dv_timings)
> #define VIDIOC_G_DV_TIMINGS _IOWR('V', 84, struct v4l2_dv_timings)
>
> Open issues
> -----------
>
> 1.How to handle an HDMI transmitter? It can be put in two different modes:
> DVI compatible
> or HDMI compatible. Some of the choices are
> a) enumerate them as two different outputs when enumerating.
> b) adding a status bit on the input.
> c) change it using a control
The same is also true for a receiver, BTW. They usually can detect whether the
input is in HDMI or DVI mode.
> 2. Detecting whether there is an analog or digital signal on an DVI-I input:
> a) add new status field value for v4l2_input ?
> #define V4L2_IN_ST_DVI_ANALOG_DETECTED 0x10000000
> #define V4L2_IN_ST_DVI_DITIGITAL_DETECTED 0x20000000
Typo: DIGITAL.
I don't think this has to be DVI specific. Just 'ST_DETECTED_ANALOG' and
ST_DETECTED_DIGITAL' should be sufficient and it is more general as well.
> 3. Detecting an EDID.
> a) adding a status field in v4l2_output and two new ioctls that can
> set the EDID for an input or retrieve it for an output. It should
> also be added as an input/output capability.
>
> 4. ATSC bits in v4l2_std_id: how are they used? Are they used at all for
> that matter?
>
>
> 6. HDMI requires additional investigation. HDMI defines a whole bunch of
> infoframe fields. Most of these can probably be exported as controls?? Is
> HDMI audio handled by alsa?
I want to add another two:
7. How to use S_DV_TIMINGS to setup a sensor.
Sensors can be setup either using the full DV_TIMINGS functionality (e.g.
pixelclock, porches, sync width, etc.) or with a subset only: width, height,
frame period. The latter can already be setup with S_PARM (but do we want
that? S_PARM is very, very ugly). I am thinking of creating a new DV_TIMINGS
type for this with just width, height and frame period.
But this leads to another complication: how to tell the user which timings
type to use? Easiest way is to use the capabilities field: CAP_BT_TIMINGS,
CAP_FRAME_TIMINGS. Of course, this limits the number of possible timings
we can define. The alternative is to add yet another field that contains
the actual timings type. But I think this is overkill.
8. Querying non-standard timings.
Currently not in this proposal. This is a complex topic and at this moment
I can't oversee all the possibilities. I know from personal experience
that this is a very difficult topic and I am not sure whether it can be
done reliably through a QUERY_DV_TIMINGS type ioctl. It may need additional
support in the form of receiver-specific ioctls.
I propose to postpone this until someone actually needs it.
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG Telecom
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