how to route gsm channel audio to processor audio channel(mcbsp)?
is it software control or hardware control?
if software control can anybody suggest me
In ICS the routing is controlled by the Audio HAL. Typically /system/hw/audio.primary.<device_name>.so. (In GB it was something similar, but different.)
Therefore, how it's handled is specific to the capabilities of the device. For example, the Audio Back-End (ABE) of OMAP 4 processors allows fairly flexible mixing and routing. It's able to move the audio directly from the modem to the audio codec (bypassing the CPU) so that it can be heard out the handsfree speaker or headset. It can also route the audio to an ALSA capture port to utilise it in userspace. These routings are usually controlled with ALSA mixer settings.
And if the hardware doesn't support it... then often the "glue" code will be added in the HAL.
I would start with looking at existing Audio HAL's. In the source tree it's usually located at device/<vendor>/<device>/audio/audio_hw.c.