[alsa-devel] Accessing already probed snd_card in kernel space

Shreshtha shreshthakumar at gmail.com
Fri Apr 15 10:27:08 CEST 2011

On Fri, Apr 15, 2011 at 1:27 PM, Clemens Ladisch <clemens at ladisch.de> wrote:

> Shreshtha wrote:
> > Vibrator hardware is connected to D-Class amplifier of Audio block.
> Does this mean that you have to generate the vibration waveform as
> sound data and write it to the sound device?  This would be rather
> unwieldy in kernel space.  (Just accessing a mixer control would be
> possible.)
> [Shreshtha] Yes that is also a use case. But I require just to enable the
vibrator for x msec and turn it off.
This is for haptic feedback.
Please suggest how to "just accessing a mixer control" from kernel?

> > But as you described that accessing from out side the sound subsystem is
> > prohibited in Kernel.
> It's not prohibited, it's just not the way the API was designed.
> [Shreshtha] So I feel even if I use the ALSA API (or OSS emulation) in
timed_output vibrator and manage to turn on the vibrator, that will not be
accepted by kernel community.

> So only way remains is to access the sound card from user space using ALSA
> > lib APIs and replace current usage of sysfs for haptic feedback. Please
> > suggest if it is right direction.
> Is the sysfs API a _required_ Android API, or would Android allow you
> to write a user space driver?
> [Shreshtha]  I found this one way of implementation seen on other devices.
There can be other, and now I feel I require one.

> Regards,
> Clemens

shreshthakumar at gmail.com

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