Re: [PATCH v3 3/4] stk1160: Add module param for setting the record gain.

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Sun, 4 Dec 2016 15:25:25 -0300
Ezequiel Garcia <ezequiel@vanguardiasur.com.ar> escreveu:

> On 4 December 2016 at 10:01, Marcel Hasler <mahasler@gmail.com> wrote:
> > Hello
> >
> > 2016-12-03 21:46 GMT+01:00 Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>:  
> >> On 2 December 2016 at 08:05, Mauro Carvalho Chehab
> >> <mchehab@s-opensource.com> wrote:  
> >>> Em Sun, 27 Nov 2016 12:11:48 +0100
> >>> Marcel Hasler <mahasler@gmail.com> escreveu:
> >>>  
> >>>> Allow setting a custom record gain for the internal AC97 codec (if available). This can be
> >>>> a value between 0 and 15, 8 is the default and should be suitable for most users. The Windows
> >>>> driver also sets this to 8 without any possibility for changing it.  
> >>>
> >>> The problem of removing the mixer is that you need this kind of
> >>> crap to setup the volumes on a non-standard way.
> >>>  
> >>
> >> Right, that's a good point.
> >>  
> >>> NACK.
> >>>
> >>> Instead, keep the alsa mixer. The way other drivers do (for example,
> >>> em28xx) is that they configure the mixer when an input is selected,
> >>> increasing the volume of the active audio channel to 100% and muting
> >>> the other audio channels. Yet, as the alsa mixer is exported, users
> >>> can change the mixer settings in runtime using some alsa (or pa)
> >>> mixer application.
> >>>  
> >>
> >> Yeah, the AC97 mixer we are currently leveraging
> >> exposes many controls that have no meaning in this device,
> >> so removing that still looks like an improvement.
> >>
> >> I guess the proper way is creating our own mixer
> >> (not using snd_ac97_mixer)  exposing only the record
> >> gain knob.
> >>
> >> Marcel, what do you think?
> >> --
> >> Ezequiel García, VanguardiaSur
> >> www.vanguardiasur.com.ar  
> >
> > As I have written before, the recording gain isn't actually meant to
> > be changed by the user. In the official Windows driver this value is
> > hard-coded to 8 and cannot be changed in any way. And there really is
> > no good reason why anyone should need to mess with it in the first
> > place. The default value will give the best results in pretty much all
> > cases and produces approximately the same volume as the internal 8-bit
> > ADC whose gain cannot be changed at all, not even by a driver.
> >
> > I had considered writing a mixer but chose not to. If the gain setting
> > is openly exposed to mixer applications, how do you tell the users
> > that the value set by the driver already is the optimal and
> > recommended value and that they shouldn't mess with the controls
> > unless they really have to? By having a module parameter, this setting
> > is practically hidden from the normal user but still is available to
> > power-users if they think they really need it. In the end it's really
> > just a compromise between hiding it completely and exposing it openly.
> > Also, this way the driver guarantees reproducible results, since
> > there's no need to remember the positions of any volume sliders.
> >  
> 
> Hm, right. I've never changed the record gain, and it's true that it
> doens't really improve the volume. So, I would be OK with having
> a module parameter.
> 
> On the other side, we are exposing it currently, through the "Capture"
> mixer control:
> 
> Simple mixer control 'Capture',0
>   Capabilities: cvolume cswitch cswitch-joined
>   Capture channels: Front Left - Front Right
>   Limits: Capture 0 - 15
>   Front Left: Capture 10 [67%] [15.00dB] [on]
>   Front Right: Capture 8 [53%] [12.00dB] [on]
> 
> So, it would be user-friendly to keep the user interface and continue
> to expose the same knob - even if the default is the optimal, etc.
> 
> To be completely honest, I don't think any user is really relying
> on any REC_GAIN / Capture setting, and I'm completely OK
> with having a mixer control or a module parameter. It doesn't matter.

If you're positive that *all* stk1160 use the ac97 mixer the
same way, and that there's no sense on having a mixer for it,
then it would be ok to remove it.

In such case, then why you need a modprobe parameter to allow
setting the record level? If this mixer entry is not used,
just set it to zero and be happy with that.

Regards,
Mauro