linux-kernel - Re: [PATCH V4 4/5] Media: Update docs for V4L2 FM new features

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Date:	Sun, 6 May 2012 21:00:09 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	manjunatha_halli@...com
Cc:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Manjunatha Halli <x0130808@...com>
Subject: Re: [PATCH V4 4/5] Media: Update docs for V4L2 FM new features

On Sat May 5 2012 00:41:34 Hans Verkuil wrote:
> > +    <table pgwide="1" frame="none" id="Radio band Types">
> > +      <title>Radio Band Types</title>
> > +      <tgroup cols="2">
> > +	&cs-str;
> > +	<tbody valign="top">
> > +		    <row>
> > +		      <entry><constant>FM_BAND_TYPE_ALL</constant>&nbsp;</entry>
> > +		      <entry>All Bands from 65.8 MHz till 108 Mhz or 162.55 MHz if weather band.</entry>
> > +		    </row>
> 
> Hmm, I have to thing about that name. And about other related issues as well:
> what to do if a band isn't supported? How does an application know which bands are
> in fact supported?
> 
> It's too late and I'll have to think about this tomorrow.

OK, I've thought about this a bit more. First of all we need a way to detect
which bands are supported. I propose to add capability flags to struct v4l2_tuner,
one for each band. There are more than enough capability flags available, so we can
start from bit 16 and add 4 capability flags for the four bands.

Since applications can now detect which bands are available, it is OK for the SEEK
ioctl to return -EINVAL if the band isn't present. Please update the SEEK ioctl
documentation accordingly.

With respect to the name FM_BAND_TYPE_ALL: I propose to rename that to _TYPE_DEFAULT.
The description should be something like:

"This is the default band, which should be the widest frequency range supported by
the hardware."

I think that is a better name since that is what drivers to at the moment. I don't
think you can guarantee an 'All bands' setting as that is often limited by the hardware.

What do you think?

Regards,

	Hans

> 
> Regards,
> 
> 	Hans
> 
> > +		    <row>
> > +		      <entry><constant>FM_BAND_TYPE_EUROPE_US</constant>&nbsp;</entry>
> > +		      <entry>Europe or US band(87.5 Mhz - 108 MHz).</entry>
> > +		    </row>
> > +		    <row>
> > +		      <entry><constant>FM_BAND_TYPE_JAPAN</constant>&nbsp;</entry>
> > +		      <entry>Japan band(76 MHz - 90 MHz).</entry>
> > +		    </row>
> > +		    <row>
> > +		      <entry><constant>FM_BAND_TYPE_RUSSIAN</constant>&nbsp;</entry>
> > +		      <entry>OIRT or Russian band(65.8 MHz - 74 MHz).</entry>
> > +		    </row>
> > +		    <row>
> > +		      <entry><constant>FM_BAND_TYPE_WEATHER</constant>&nbsp;</entry>
> > +		      <entry>Weather band(162.4 MHz - 162.55 MHz).</entry>
> > +		    </row>
> > +	</tbody>
> > +      </tgroup>
> > +    </table>
> >  
> >    <refsect1>
> >      &return-value;
> > 
> 
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