Re: [PATCH v2 1/7] v4l2: video device: Add V4L2_CTRL_CLASS_FMTX controls

[Eduardo Valentin <eduardo.valentin@nokia.com>]

On Tue, May 12, 2009 at 12:29:54PM +0200, ext Mauro Carvalho Chehab wrote:
> Em Tue, 12 May 2009 08:26:40 +0200
> Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> 
> > The only reason why such a table might end up in the kernel is if there are 
> > legal requirements forcing strict control on what is allowed for an FM 
> > transmitter in each country, and in that case a similar mechanism as is 
> > used for wifi should be used. I know we discussed this earlier, but I've 
> > forgotten the exact name of that API.
> 
> If the usage of FM transmission is for very short range transmissions (for
> example, to listen to a phone call inside your car stereo, or to listen to your
> baby's room noises or to see him while you're in the kitchen), I doubt that
> there are any legal requirements. Such usage is called by the regulatory
> agencies as "secondary usage"[1]. The secondary usage for FM and for their
> adjacent frequencies (the TV range) should allow such domestic usage [2]. In
> general, the restriction for secondary usage is just the power level, to avoid
> interferences with the primary usage. In general, the secondary usage for TV
> and FM ranges are the same (and both ranges are adjacent).
> 
> On the other hand, for FM primary usage, e. g. a FM broadcaster, the
> restriction is that you should transmit _ONLY_ at the authorized frequency, at
> the specified maximum power (that may have a different max power during the day
> or during the night), using strict shapes for frequency shift, and for
> modulation levels. It also restricts the location of the FM station, and the
> characteristics of the antenna beams. Such constraints require application,
> infrastructure and hardware control that couldn't be done at kernel level.
> 
> So, I don't see how legal issues might affect this driver.
> 
> [1] Maybe the specific term may change from country to country, but the idea
> remains the same, since this concept exists on ITU-R regulations.
> 
> [2] I'm not aware of any country that forbids the usage of FM/TV ranges for
> domestic usage. Yet, if such country does exist, then the usage of this module
> should be forbidden at such country, no matter what frequency you're
> generating. So, again, it seems pointless to add such restriction in kernel.

Right. I've to agree that there is no need to have those in kernel. Better
to leave this role to user land, if some legal requirement is needed then.
I'll resend the patches without the region settings. It will export only
the device limits. I believe that user land can, on top of that, handle
the channel spacing and frequency limits. Of course, leaving a way to set/get
the preemphasis will be kept. But not bound to a region setting anymore.

> 
> Cheers,
> Mauro

Cheers,

-- 
Eduardo Valentin