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

[Antti Palosaari <crope@iki.fi>]

On 12.03.2014 14:47, Mauro Carvalho Chehab wrote:
> Em Wed, 12 Mar 2014 14:26:35 +0200
> Antti Palosaari <crope@iki.fi> escreveu:
>
>> 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.
>
> Well, on DVB, the bandwidth is specified in Hz, at DVBv5 (or via
> an enum on DVBv3).
>
> Here, there's no description about the unit to be used (Hz? kHz?).
> It just says that this is an integer, with a driver-specific
> range and step.
>
> So, one driver might choose to use Hz, other kHz, and other to
> expose some internal counter. That's bad.
>
> We should either use a V4L2_CTRL_TYPE_MENU type of control, where it
> would be possible to do something similar to DVBv3 way to specify
> the bandwidth filter, or to define that the bandwidth will be
> in Hz, kHz or MHz.

Yeah, indeed. That was my mistake. The aim was Hz yes.

>
> Probably, a menu type is better, as it allows userspace to get
> all supported bandwidths.

I though it too, but there is already a lot choices for some tuners, 
E4000 has over 30. What is maximum reasonable filter count for 
V4L2_CTRL_TYPE_MENU?

regards
Antti

-- 
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