[alsa-devel] [PATCH 1/2] snd-maestro3: Make hardware volume buttons an input device

Takashi Iwai tiwai at suse.de
Thu Apr 22 17:02:12 CEST 2010

At Thu, 22 Apr 2010 04:37:04 -0400,
Hans de Goede wrote:
> While working on the sound suspend / resume problems with my laptop
> I noticed that the hardware volume handling code in essence just detects
> key presses, and then does some hardcoded modification of the master volume
> based on which key is pressed.
> This made me think that clearly the right thing to do here is just report
> these keypresses to userspace as keypresses using an input device and let
> userspace decide what to with them.
> This patch does this, getting rid of the ugly direct ac97 writes from
> the tasklet, the ac97lock and the need for using a tasklet in general.
> As an added bonus the keys now work identical to volume keys on a (usb)
> keyboard with multimedia keys, providing visual feedback of the volume
> level change, and a better range of the volume control (with a properly
> configured desktop environment).

I like the basic idea.  However, two points to be fixed:

 - We need a kconfig to keep the old behavior.  We are not allowed to
   give any regression in general.

 - CONFIG_INPUT is tristate.  It can be a module, thus the dependency
   is a bit messy.  Imagine you want to build snd-maestro3 into kernel
   while CONFIG_INPUT=m is given.
A hack to avoid to avoid the dependency is to create a bool Kconfig to
specify whether input feature is added or not; this is anyway needed
for the first reason above.  Suppose it CONFIG_SND_MAESTRO3_INPUT.

Then it looks like:

	bool "enable input device for maestro3 volume switches"
	depends on SND_MAESTRO3
	depends on INPUT=y || INPUT=SND_MAESTRO3

Then you can use "#ifdef CONFIG_SND_MAESTRO3_INPUT" to determine
compile condition.  If this isn't defined, keep the old behavior,
i.e. controlling ac97 registers directly.



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