Re: [PATCH RFC v2] media: OF: add sync-on-green endpoint property

[Sylwester Nawrocki]

Hi,

On 05/25/2013 11:17 AM, Prabhakar Lad wrote:
> >  From looking at Figure 8 "TVP7002 Application Example" in the TVP7002's
> > >  datasheet
> > >  ([2], p. 52) and your initial TVP7002 patches it looks like what you want is
> > >  to
> > >  specify polarity of the SOGOUT signal, so the processor that receives this
> > >  signal
> > >  can properly interpret it, is it correct ?
> > >
> Yes
> > >  If so then wouldn't it be more appropriate to define e.g. 'sog-active'
> > >  property
> > >  and media bus flags:
> > >           V4L2_MBUS_SYNC_ON_GREEN_ACTIVE_LOW
> > >           V4L2_MBUS_SYNC_ON_GREEN_ACTIVE_HIGH
> > >  ?
> > >
> Agreed I'll add these flags.
>
> > >  And for synchronisation method on the analog part we could perhaps define
> > >  'component-sync' or similar property that would enumerate all possible
> > >  synchronisation methods. We might as well use separate boolean properties,
> > >  but I'm a bit concerned about the increasing number of properties that need
> > >  to be parsed for each parallel video bus "endpoint".
> > >
> I am not clear on it can please elaborate more on this.

I thought about two possible options:

1. single property 'component-sync' or 'video-sync' that would have values:

#define VIDEO_SEPARATE_SYNC	0x01
#define VIDEO_COMPOSITE_SYNC	0x02
#define VIDEO_SYNC_ON_COMPOSITE	0x04
#define VIDEO_SYNC_ON_GREEN	0x08
#define VIDEO_SYNC_ON_LUMINANCE	0x10

And we could put these definitions into a separate header, e.g.
<dt-bindings/video-interfaces.h>

Then in a device tree source file one could have, e.g.

video-sync = <VIDEO_SYNC_ON_GREEN>;


2. Separate boolean property for each video sync type, e.g.

	"video-composite-sync"
	"video-sync-on-composite"
	"video-sync-on-green"
	"video-sync-on-luminance"

Separate sync, with separate VSYNC, HSYNC lines, would be the default, when
none of the above is specified and 'vsync-active', 'hsync-active' properties
are present.

However, I suppose the better would be to deduce the video synchronisation
method from the sync signal polarity flags. Then, for instance, when an
endpoint node contains "composite-sync-active" property the parser would
determine the "composite sync" synchronisation type is used.

Thus it might make sense to have only following integer properties (added
as needed):

composite-sync-active
sync-on-green-active
sync-on-comp-active
sync-on-luma-active

This would allow to specify polarity of each signal and at the same time
the parsing code could derive synchronisation type. A new field could be
added to struct v4l2_of_parallel_bus, e.g. sync_type and it would be filled
within v4l2_of_parse_endpoint().

What do you think ?


Thanks,
Sylwester
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