Re: [REVIEW PATCH 11/13] DocBook: document RF tuner bandwidth controls

[Antti Palosaari <crope@iki.fi>]

On 12.03.2014 14:26, Antti Palosaari wrote:
> On 12.03.2014 13:02, Mauro Carvalho Chehab wrote:
>> Em Mon, 10 Mar 2014 12:01:28 +0200
>> Antti Palosaari <crope@iki.fi> escreveu:
>>
>>> On 05.03.2014 20:49, Mauro Carvalho Chehab wrote:
>>>> Em Thu, 27 Feb 2014 02:22:06 +0200
>>>> Antti Palosaari <crope@iki.fi> escreveu:
>>>>
>>>>> Add documentation for RF tuner bandwidth controls. These controls are
>>>>> used to set filters on tuner signal path.
>>>>>
>>>>> Cc: Hans Verkuil <hverkuil@xs4all.nl>
>>>>> Signed-off-by: Antti Palosaari <crope@iki.fi>
>>>>> ---
>>>>>    Documentation/DocBook/media/v4l/controls.xml | 19
>>>>> +++++++++++++++++++
>>>>>    1 file changed, 19 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/DocBook/media/v4l/controls.xml
>>>>> b/Documentation/DocBook/media/v4l/controls.xml
>>>>> index 6c9dbf6..5550fea 100644
>>>>> --- a/Documentation/DocBook/media/v4l/controls.xml
>>>>> +++ b/Documentation/DocBook/media/v4l/controls.xml
>>>>> @@ -5007,6 +5007,25 @@ descriptor. Calling &VIDIOC-QUERYCTRL; for
>>>>> this control will return a
>>>>>    description of this control class.</entry>
>>>>>                </row>
>>>>>                <row>
>>>>> +              <entry
>>>>> spanname="id"><constant>V4L2_CID_RF_TUNER_BANDWIDTH_AUTO</constant>&nbsp;</entry>
>>>>>
>>>>> +              <entry>boolean</entry>
>>>>> +            </row>
>>>>> +            <row>
>>>>> +              <entry spanname="descr">Enables/disables tuner radio
>>>>> channel
>>>>> +bandwidth configuration. In automatic mode bandwidth configuration
>>>>> is performed
>>>>> +by the driver.</entry>
>>>>> +            </row>
>>>>> +            <row>
>>>>> +              <entry
>>>>> spanname="id"><constant>V4L2_CID_RF_TUNER_BANDWIDTH</constant>&nbsp;</entry>
>>>>>
>>>>> +              <entry>integer</entry>
>>>>> +            </row>
>>>>> +            <row>
>>>>> +              <entry spanname="descr">Filter(s) on tuner signal
>>>>> path are used to
>>>>> +filter signal according to receiving party needs. Driver
>>>>> configures filters to
>>>>> +fulfill desired bandwidth requirement. Used when
>>>>> V4L2_CID_RF_TUNER_BANDWIDTH_AUTO is not
>>>>> +set. The range and step are driver-specific.</entry>
>>>>
>>>> Huh? If this is enable/disable, why "the range and step are
>>>> driver-specific"?
>>>
>>> Because there is two controls grouped. That is situation of having
>>> AUTO/MANUAL.
>>> V4L2_CID_RF_TUNER_BANDWIDTH_AUTO
>>> V4L2_CID_RF_TUNER_BANDWIDTH
>>>
>>> V4L2_CID_RF_TUNER_BANDWIDTH is valid only when
>>> V4L2_CID_RF_TUNER_BANDWIDTH_AUTO == false.
>>>
>>
>> Sorry, but I'm not understanding what you're arguing.
>>
>> Yeah, it is clear at the patch that there are two controls, and that
>> V4L2_CID_RF_TUNER_BANDWIDTH is valid only when AUTO is disabled, but
>> this doesn't answer my question:
>>
>> Why V4L2_CID_RF_TUNER_BANDWIDTH's range and step are driver-specific?
>>
>
> Hmmm. That control is used to configure RF filters. Filters set
> bandwidth of radio channel. There is usually quite limited set of
> available analog filters inside RF tuner. If you look for example
> FC0012/FC0013 possible filters are 6/7/8 MHz. E4000 has something 4-11
> MHz. If you look those very old 1st gen silicon tuners like QT1010 /
> MT2060, there is no integrated filters at all - but there is external
> saw filter which is usually 8MHz at 36.125 MHz IF.
>
> Did you remember there is same parameter already in DVB API (struct
> dtv_frontend_properties bandwidth_hz)? That is control is currently used
> to set r820t, fc0012, fc10013 .bandwidth_hz value, e4000 implements it
> correctly as own control.
>
> I am quite astonished we have that big gap with our views.

Here is picture from GNU Radio UHD source (it is the original Ettus HW 
GNU Radio was done AFAIK). Bandwidth is last control.

http://lists.gnu.org/archive/html/discuss-gnuradio/2010-12/pngqfPrwUmgsB.png

regards
Antti

-- 
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