Date:	Tue, 13 Mar 2012 10:20:27 -0500
From:	halli manjunatha <manjunatha_halli@...com>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Manjunatha Halli <x0130808@...com>, shahed@...com
Subject: Re: [PATCH 3/3] wl128x: Add sysfs based support for FM features

On Sat, Mar 10, 2012 at 3:56 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
> On Friday, March 09, 2012 21:44:10 halli manjunatha wrote:
>> On Fri, Mar 9, 2012 at 2:29 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
>> > On Wednesday, March 07, 2012 22:42:05 halli manjunatha wrote:
>> >> On Mon, Mar 5, 2012 at 10:24 AM, halli manjunatha <hallimanju@...il.com> wrote:
>> >> > On Fri, Mar 2, 2012 at 3:22 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
>> >> >> On Wednesday, February 29, 2012 18:19:27 halli manjunatha wrote:
>> >> >>> On Wed, Feb 29, 2012 at 5:25 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
>> >> >>> > On Tuesday, February 28, 2012 23:52:21 halli manjunatha wrote:
>> >> >>> >> On Tue, Feb 28, 2012 at 4:05 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
>> >> >>> >> > On Monday, February 27, 2012 17:29:18 halli manjunatha wrote:
>> >> >>> >> >> Hi Hans,
>> >> >>> >> >>
>> >> >>> >> >> Agreed I don't mind to create new controls for below things
>> >> >>> >> >>
>> >> >>> >> >> 1) FM RX Band selection (US/Europe, Japan and Russian bands)
>> >> >>> >> >> 2) FM RX RDS AF turn ON/OFF
>> >> >>> >> >> 3) FM RX RSSI level set/get
>> >> >>> >> >> 4) FM TX Alternate Frequency set/get
>> >> >>> >> >> 5) FM RX De-Emphasis mode set/get
>> >> >>> >> >>
>> >> >>> >> >> However, previously you have suggested me to hide few controls (like
>> >> >>> >> >> band selection) from the user but few of our application wanted
>> >> >>> >> >> controls like above and that is why I have created the sysfs entries.
>> >> >>> >> >>
>> >> >>> >> >> Please suggest me how can I move forward with new controls or with sysfs?
>> >> >>> >> >
>> >> >>> >> > The first question is which of these controls are general to FM receivers or
>> >> >>> >> > transmitters, and which are specific to this chipset. The chipset specific
>> >> >>> >> > controls should be private controls (look at V4L2_CID_MPEG_CX2341X_BASE in
>> >> >>> >> > videodev2.h how those are defined). The others should be defined as new
>> >> >>> >> > controls of the FM_TX class or the FM_RX class. The FM_RX class should be
>> >> >>> >> > defined as a new class as it doesn't exist at the moment. Don't forget to
>> >> >>> >> > document these controls clearly.
>> >> >>> >> >
>> >> >>> >> > With regards to the band selection: I remember that there was a discussion,
>> >> >>> >> > but not the details. Do you have a link to that discussion? I can't find it
>> >> >>> >> > (at least not quickly :-) ).
>> >> >>> >>
>> >> >>> >> Below features are generic to all FM receivers so we can add new CID's
>> >> >>> >> for below features
>> >> >>> >> 1) FM RX RDS AF turn ON/OFF
>> >> >>> >> 2) FM TX Alternate Frequency set/get
>> >> >>> >>
>> >> >>> >> About other 3 features its different issue,
>> >> >>> >>     1) FM RX Band selection (US/Europe, Japan and Russian bands)
>> >> >>> >>     2) FM RX RSSI level set/get
>> >> >>> >>     3) FM RX De-Emphasis mode set/get
>> >> >>> >>
>> >> >>> >> All these 3 features are generic to any FM receiver, only question is
>> >> >>> >> does all FM receivers wants to expose these controls to application
>> >> >>> >> writer?
>> >> >>> >
>> >> >>> > Good question, and there is no good answer at the moment. See e.g. this
>> >> >>> > IRC discussion:
>> >> >>> >
>> >> >>> > http://www.spinics.net/lists/linux-media/msg44023.html
>> >> >>> >
>> >> >>> > In the absence of a good solution to this problem I am inclined to make
>> >> >>> > these controls driver specific but marked experimental. The experimental
>> >> >>> > tag allows us to eventually make it a generic control without too much
>> >> >>> > hassle.
>> >> >>>
>> >> >>> Agreed, I will make them driver specific and mark them as experimental.
>> >> >>>
>> >> >>> >
>> >> >>> >> Example Band selection, every FM receiver at the minimum supports both
>> >> >>> >> Europe and Japan band, now the question is should we add a CID to
>> >> >>> >> switch between these two bands?
>> >> >>> >
>> >> >>> > If we decide to add a band selection control, then that would be a menu
>> >> >>> > control (since there are up to three bands) and it would only be implemented
>> >> >>> > by drivers that need it.
>> >> >>> >
>> >> >>> > What I am still not clear on is *why* you would want this control. What
>> >> >>> > is the reason your customers want this? What does it allow you to do that
>> >> >>> > can't be done today?
>> >> >>>
>> >> >>> There are 2 reasons for this,
>> >> >>>
>> >> >>> First, our chip supports weather band, unlike other bands (Europe,
>> >> >>> Japan and Russian) user may wants to
>> >> >>> switch to weather band and wants to listen to weather report and again
>> >> >>> switches back to normal band.
>> >> >>
>> >> >> OK, that makes sense. Are the RX and TX independent with regards to
>> >> >> band selection?
>> >> >
>> >> > Yes - RX and TX are independent of band selection
>> >> >
>> >> >> Make sure that when the band is changed the rangelow and rangehigh values
>> >> >> are also changed. If the current frequency is out of that range, then the
>> >> >> frequency should be clamped to the closest value frequency. Although an
>> >> >> alternative strategy might be to remember the last used frequency for each
>> >> >> band. That might make more sense in the case of switching between a normal
>> >> >> band and the weather band. We need to define and document which strategy
>> >> >> should be used here.
>> >> >
>> >> > As of now when I switch to new band I just set the frequency to lowest
>> >> > of the new band.
>> >> > In this way user can seek and tune to what ever channel he wants.
>> >> >
>> >> Hans,
>> >>
>> >> Which implementation you wants? start with the lowest of the new band
>> >> or closer to the frequency of old band? do we need to remember the
>> >> present frequency of the band before switching to new band?
>> >>
>> >> Please let me know your views.
>> >
>> > The initial frequency of each band is driver dependent. That's how drivers
>> > act at the moment, so we keep that.
>> >
>> > When switching bands it is best to keep the frequency closest to the old band.
>> > This makes sense when switching from e.g. US/Europe and Japan band where there
>> > is overlap in frequencies, so I think that's the best approach.
>> >
>> >> Since this feature is required by all FM receivers shall I make this
>> >> as a generic CID?
>> >
>> > Yes, but see my next question below.
>> >
>> >>
>> >> >> BTW, is the receiver for the weather band implemented as a separate receiver?
>> >> >> I read that some devices can listen to the normal band and interrupt that
>> >> >> when a weather report is broadcast on the weather band. That implies two
>> >> >> receivers and it would require a rethink.
>> >> >>
>> >> >> Also, is this feature really implemented as separate frequency ranges in
>> >> >> hardware? Or is the receiver able to receive on the whole range of frequencies
>> >> >> from 65.8 (OIRT) to approx. 165 (weather band range)?
>> >> >
>> >> > Our chip wont have 2 receivers, it has only 1 receiver which can
>> >> > receive on whole frequency range from 65 MHz to 165 MHz.
>> >
>> > If that's the case, then what does the band selector control actually have to do
>> > hardware-wise? Does it just clamp the frequency to the correct frequency range?
>>
>> The Wilink chip can't able to receive on all frequencies at a time,
>> instead first we need to set the band(need to set chip registers to do
>> so) on which receiver has to receive, after this the chip can receive
>> on frequency range of this band only.
>>
>> Eg: When set to Europe band chip can only receive from 87.5 MHz to 108
>> MHz, in this case receiver will give band limit reached interrupt if
>> tried to set frequency other than within this band.
>>
>> Band selector controller will first switch the band of reception and
>> then sets the frequency which is within that band.
>>
>> >
>> >> >
>> >> >> Is the datasheet of this device available somewhere?
>> >> >
>> >> > Sorry our newest chipset supports this feature so yet now we don't
>> >> > have any datasheet available on net.
>> >> >
>> >> >>
>> >> >>> Second,  for FM TX, our chip supports band selection for FM
>> >> >>> transmitter, so if the same phone is used in different
>> >> >>> regions of world then user can switch to the actual band and start
>> >> >>> transmitting by choosing a blank frequency in that band.
>> >> >>
>> >> >> Isn't this something that can be equally easily done in userspace?
>> >> >
>> >> > you wants me to do this from driver itself without hinting the
>> >> > application about the band ?
>> >
>> > I think my question is really the same as above: what does the band selector
>> > control actually have to do for a TX hardware-wise?
>>
>> Yes TX case I accept we may not need the band switch controller,
>> instead when user wants to set a frequency, driver will see in which
>> band this frequency comes and then first switches the FM chip to
>> transmit in that band and then sets the frequency.
>>
>> So I don't add any private or public CID for this.
>
> Good.
>
>> >
>> > None of the existing radio RX and TX drivers need a band selector, because
>> > they just cover the whole frequency range. If apps want to create these bands,
>> > then they can do so themselves. So I am trying to understand why this device
>> > needs a band selector. It's why I was interested in the datasheet...
>>
>> In RX case the the above provided solution wont work because
>> 1) If user do hardware seek then seek will be performed within the
>> present band not throughout from 65MHz to 162 MHz
>> 2) If user wants to switch band he should know the frequency range of
>> the band to which he is switching and then set the frequency within
>> that band.
>>
>> Hardware seek functionality is one of the main reason why we need band
>> switch, most of the time user may not have knowledge about the
>> frequency ranges of bands so in that case use will switch to a band
>> and do hardware seek, if stations found then he will continue on the
>> same band if not he can check the next available band and do seek
>> again.
>
> How about this: rather than adding a band selection control, why not add a
> new band field to struct v4l2_hw_freq_seek? The default, 0, means just use the
> full frequency range. Then define the other bands (these are pretty much
> standardized). If a band is not supported by the hardware, -ERANGE is returned.
> Otherwise the current frequency is clamped to the specified band frequency range
> and you start searching.
>
> Band selection doesn't really make sense outside of hardware seek.

Looks fine for me... I will continue with this approach and submit the
next patch set :)

>
> Regards,
>
>        Hans
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