[alsa-devel] PC Beep or PC Speaker or just Beep? and HDA Beep code...

[Takashi Iwai]

At Tue, 3 Nov 2009 12:01:57 +0100 (CET),
Jaroslav Kysela wrote:
> 
> On Fri, 30 Oct 2009, Takashi Iwai wrote:
> 
> > At Thu, 22 Oct 2009 17:50:10 +0200 (CEST),
> > Jaroslav Kysela wrote:
> >>
> >> Hi,
> >>
> >>  	I'm changing the behaviour of Beep / PC Beep controls for HDA
> >> drivers (comments?):
> >>
> >> http://git.alsa-project.org/?p=alsa-kernel.git;a=commitdiff;h=d605dbeed1b102136513e09e95217e8dc19c800d
> >
> > Well, IMHO, the fundamental problem is that there is no logic to
> > select the beep device in the input layer.  A few line of code to
> > drivers/char/keyboard.c would do that.
> 
> Yes, it would be good to have possibility to configure which input device 
> will receive beep events.

I had even a patch somewhere... I need to dig down my archive.

> > Regarding your change: I'm afraid that too frequent attach/detach
> > calls aren't good.
> 
> What's too frequent? The attach/detach is called only when Beep mute 
> control is toggled. I don't think that user will toggle this control as 
> more as once in a normal system setup. The default value is "muted" 
> (no registration) anyway.

Heh, you can't expect how odd things users would do.
I can foresee this too frequent toggling can happen simply, e.g. key
auto-repeating on a mute button.

> I would really like to have the HDA Beep registration to input layer 
> configurable at runtime. The control layer seems good for this job.
> I can eventually add one more control with name like "Beep Register 
> Switch", but the "Beep Playback Switch" does this job well.

Well, the biggest problem in your patch is that its re-register the
input device.  When you watch the kernel message, you'll find that the
new input device is added at each time you toggle the beep switch,
  input: HDA Digital PCBeep as /devices/pci0000:00/0000:00:1b.0/input/input6
  input: HDA Digital PCBeep as /devices/pci0000:00/0000:00:1b.0/input/input7
  ...
With frequent toggles, you can reach to a very high number very
easily.

> >  Also, note that there are hardwares that still
> > beep even when the beep volume is set to zero.  So, you may get a
> > situation that you can't disable beep tone.
> 
> ??? If you don't set HDA codec frequency registers, then the HDA 
> digital beep cannot be generated.

It's a scenario like below:
  - "Beep Playback Switch" off -> pcspr is activated; no way to
    control the beep volume -> beep always heard
  - "Beep Playback Switch" on -> HD-audio beep active; but it's still
    audible even when "Beep Playback Volume" is zero -> beep always
    heard

So, in this case, you can't kill beep tones.


thanks,

Takashi