linux-kernel - Re: [PATCH v2 2/2] media: i2c: tvp7002: add OF support

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Message-ID: <51E2FF42.2090507@gmail.com>
Date:	Sun, 14 Jul 2013 21:42:58 +0200
From:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>
To:	Prabhakar Lad <prabhakar.csengg@...il.com>
CC:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	LMML <linux-media@...r.kernel.org>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Sakari Ailus <sakari.ailus@....fi>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH v2 2/2] media: i2c: tvp7002: add OF support

Hi Prabhakar,

On 07/12/2013 06:43 AM, Prabhakar Lad wrote:
> On Fri, Jul 12, 2013 at 3:34 AM, Sylwester Nawrocki
> <sylvester.nawrocki@...il.com>  wrote:
>> On 07/11/2013 07:09 PM, Prabhakar Lad wrote:
[...]
>>>> And include/media/tvp70002.h:
>>>>
>>>>    * fid_polarity:
>>>>    *                      0 ->   the field ID output is set to logic 1 for
>>>> an
>>>> odd
>>>>    *                           field (field 1) and set to logic 0 for an
>>>> even
>>>>    *                           field (field 0).
>>>>    *                      1 ->   operation with polarity inverted.
>>>>
>>>>
>>>> Do you know if the chip automatically selects video sync source
>>>> (sync-on-green
>>>> vs. VSYNC/HSYNC) and there is no need to configure this on the analogue
>>>> input
>>>> side ? At least the driver seems to always select the default SOGIN_1
>>>> input
>>>> (TVP7002_IN_MUX_SEL_1 register is set only at initialization time).
>>>>
>>> Yes the driver is selecting the default SOGIN_1 input.
>>>
>>>> Or perhaps it just outputs on SOGOUT, VSOUT, HSOUT lines whatever is fed
>>>> to
>>>> its analogue inputs, and any further processing unit need to determine
>>>> what
>>>> synchronization signal is present and should be used ?
>>>>
>>>
>>> Yes that correct, there is a register (Sync Detect Status) which
>>> detects the sync for you.
>>>
>>>> I suspect that we don't need, e.g. another endpoint node to specify the
>>>> configuration of the TVP7002 analogue input interface, that would contain
>>>> a property like video-sync.
>>>>
>>>>
>>> If I understand correctly you mean if there are two tvp7002 devices
>>> connected
>>> we don’t need to specify video-sync property, but my question how do we
>>> specify this property in common then ?
>>
>>
>> No, I thought about two port sub-nodes of a single device node, one for the
>> TVP7002 video input and one for the output. But it seems there is no need
>> for that, i.e. to specify the input configuration statically in the
>> firmware.
>> The chip detects the signals automatically, i.e. it uses whatever is
>> available,
>> and it allows querying the selection status at run time. What would really
>> need to be configured statically in DT in that case then ? Some initial
>> video
>> sync configuration ? I guess it could be well hard coded in the driver,
>> since
>> the hardware does run time detection anyway.
>>
> Yes the chip detects the signal automatically, What I want to configure in
> the DT case is say if SOG signal is detected, I want to invert the polarity
> of it this is what I am trying to set in DT case whether to invert or not.
> 0 = Normal operation (default)
> 1 = SOG output polarity inverted
>
> Something similar to fid_polarity.

Then as I suggested earlier, let's just add 'sync-on-green-active' DT
property for that. I wouldn't expect the DT properties to be directly
replacing your driver platform_data members. Saying in the binding that
this is a normal operation and that is an inverted one is not very useful
in general, as you would need to dig in the binding's description what
"normal" exactly means. sync-on-green-active = <1>; seems much more
explicit than, e.g. sync-on-green-inverted. By looking at the
sync-on-green-active property each device driver would determine whether
it means normal or inverted operation for its device.

--
Thanks,
Sylwester
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