Re: [PATCH 0/3] cxd2820r: tweak search algorithm, enable LNA in DVB-T mode

[Antti Palosaari <crope@iki.fi>]

On 15.03.2012 19:41, Mauro Carvalho Chehab wrote:
> Em 15-03-2012 14:33, Gianluca Gennari escreveu:
>> The PCTV 290e had several issues on my mipsel-based STB (powered by a
>> Broadcom 7405 SoC), running a Linux 3.1 kernel and the Enigma2 OS.
>>
>> The most annoying one was that the 290e was able to tune the lone DVB-T2
>> frequency existing in my area, but was not able to tune any DVB-T channel.
>>
>> Following a suggestion of the original author of the driver, I tried to
>> tweak the wait time in the lock loop. In fact, increasing the wait time
>> from 50 to 200ms in the tuning loop was enough to get the lock on most
>> channels.
>> But channel change was quite slow and sometimes, doing an automatic scan,
>> some frequency was not locked.
>> So instead of playing with the timings I changed the behavior of the
>> search algorithm as explained in the patch 1, with very good results.
>>
>> With this modification, the automatic scan is 100% reliable and zapping
>> is quite fast (on the STB). There is no noticeable difference when using
>> Kaffeine on the PC.
>>
>> But there was a further issue: a few weak channels were affected by high
>> BER and badly corrupted pictures. The same channels were working fine on
>> an Avermedia A867 stick (as well as other sticks).
>>
>> The driver has an option to enable a "Low Noise Amplifier" (LNA) before the
>> demodulator. Enabling it, the reception of weak channels improved a lot,
>> as reported in the description of patch 2.
>
> Hi Gianluca,
>
> With regards to LNA, the better is to add a DVBv5 property for it.
>
> The LNA is generally located at the antenna, and not at the device.

LNA inside antenna, or near antenna, is called amplifier. Power to that 
amplifier is feed by device or power supply using antenna cable.

I see LNA more likely amplifier that is inside device. It could be 
external chip between tuner IC and antenna connector or more usually 
logical part inside tuner IC.

Thus I see two different use cases here. 1) LNA, 2) power supply to 
amplifier.

> As you know, more than one device may be connected to the same antenna,
> and it is generally not a good idea to have two devices sending power to
> the LNA.
>
> So, it is better to have a way to turn it on via the usespace API.
>
> Also, as this consumes power, the better is to do it only when the device
> is actually used.

I think we need API support for LNA/amp + internal API support for AUTO LNA.

Originally I added LNA support as a module param for em28xx-dvb but 
Mauro NACKed it thus it is hard coded. Anyhow, some method switching LNA 
on/off is better than no method at all.

regards
Antti

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