Re: [git:v4l-dvb/for_v3.7] [media] add LNA support for DVB API

[Antti Palosaari <crope@iki.fi>]

On 09/28/2012 08:07 PM, Hans Verkuil wrote:
> On Fri September 28 2012 17:30:05 Mauro Carvalho Chehab wrote:
>> Em Fri, 28 Sep 2012 16:21:35 +0200
>> Hans Verkuil <hverkuil@xs4all.nl> escreveu:
>>
>>> On Fri September 28 2012 14:43:32 Hans Verkuil wrote:
>>>> Hi Antti,
>>>>
>>>> Mauro asked me to look into LNA as well, in particular how this could be done
>>>> on the analog side as well.
>>
>> Thanks for that!
>>
>>>>
>>>> While reading through this patch I noticed that the new property was added to
>>>> dtv_property_process_set, but not to dtv_property_process_get. Can you look
>>>> into that and add 'get' support for this property?
>>>
>>> It's a sign of insanity when you start replying to your own email, but so
>>> be it :-)
>>
>> :)
>>
>>>
>>> I've been thinking how this can be implemented in such a way that it works
>>> well in all the various board/tuner configurations.
>>>
>>> First, the property should be cached in dtv_frontend_properties, that way
>>> tuners with a built-in LNA can use it. The initial value should be AUTO,
>>> I guess.
>>>
>>> The property_process_set code changes to:
>>>
>>> 	case DTV_LNA:
>>> 		if (fe->ops.set_lna)
>>> 			r = fe->ops.set_lna(fe, tvp->u.data);
>>> 		if (!r)
>>> 			c->lna = tvp->u.data;
>>> 		break;
>>>
>>> Tuners can now check the c->lna value when set_params is called and take the
>>> appropriate steps if they have a built-in LNA.
>>>
>>> To be able to access the LNA from the V4L2 side you would need to add two
>>> new tuner ops in include/media/v4l2-subdev.h:
>>>
>>> 	int (*g_lna)(struct v4l2_subdev *sd, u32 *lna);
>>> 	int (*s_lna)(struct v4l2_subdev *sd, u32 lna);
>>>
>>> The tuner-core.c driver can implement these ops to get and set c->lna accordingly.
>>>
>>> A menu control would be needed to actually change the LNA.
>>>
>>> The code that handles that control would have to call a board-specific function
>>> if necessary (if the LNA is on the board), and call the tuner's s_lna op otherwise.
>>>
>>
>> Makes sense.
>>
>>>> The only question is whether the digital and analog APIs should share the same
>>> LNA setting or keep different LNA states for each.
>>>
>>> So if I call DTV_LNA to set the LNA, and then check the LNA control value from V4L2,
>>> should the two match? Or should we keep separate states and whenever you select
>>> digital or analog mode the LNA is updated with the corresponding LNA value for that
>>> mode.
>>>
>>> The latter is a bit more work (struct analog_parameters should probably be extended
>>> with an LNA value), but I do think it is a cleaner solution.
>>
>> I think they both should share the same LNA state, as this depends on the physical
>> connection (e. g. if the antenna has LNA; if the signal reception is weak or strong
>> with that particular antenna).
>>
>>> I am not sure if the LNA work on the analog side should be done without having
>>> hardware that actually uses it, but at least the LNA support on the digital side
>>> should be done in such a way that it can be extended for analog as well.
>>
>> There are several saa7134 hardware with LNA support. I have one of such boards
>> here, although never needed to dig into the LNA stuff on it.
>
> I'll wait until Antti makes the necessary changes on the digital side, after that
> I'll see if I can make a patch for the analog part, and post that. There is an
> outside chance that I have a board with an LNA as well: for ivtv there were issues
> with a Samsung TCPN 2121P30A tuner where the LNA had to be turned on or off manually
> (it should have been automatic but due to a hardware bug that didn't work). This
> was never supported in ivtv, but this would make a good test case.
>
> The only problem is that I don't know if I still have that card or if I gave it
> to Andy. I think it went to him, actually.

Hans, your changes moving lna to property cache is fine for my eyes. I 
can change it if you wish, but maybe Sunday or next week

I dropped get operation originally as I wanted to keep workload small on 
that time. Also there was some other design issues, like one I selected 
AUTO as minimum possible value to leave space for extending possible 
values (both attenuation and gain). For now it is just on/off, but there 
is existing LNAs having more gain levels, not to mention VGAs and LNAs 
integrated to RF-tuners. Other design issue was units. Gains are 
measured as units of decibels, but I decided to use device specific 
steps instead of making some mechanism to enumerate supported gain levels.

Here is some discussion behind that LNA.

http://www.spinics.net/lists/linux-media/msg50132.html
http://www.spinics.net/lists/linux-media/msg50133.html
http://www.spinics.net/lists/linux-media/msg50139.html

http://blog.palosaari.fi/2012/07/patch-rfc-add-lna-support-for-dvb-api.html

regards
Antti
-- 
http://palosaari.fi/