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

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Date:	Sat, 25 May 2013 16:11:52 +0200
From:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>
To:	Prabhakar Lad <prabhakar.csengg@...il.com>
CC:	LMML <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Sakari Ailus <sakari.ailus@....fi>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH RFC v2] media: OF: add sync-on-green endpoint property

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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