The first patch implements McBSP sidetone feature on OMAP3 while the second one provides ALSA interface for using it.
The patch set is based on the patch Eduardo Valentin sent to alsa-devel mailing list in October 2009. Channel gain control and enabling the sidetone have been moved to ALSA interface as suggested in comments.
Eero Nurkkala (1): McBSP: OMAP3: Add sidetone feature
Ilkka Koskinen (1): ASoC: OMAP-McBSP: ASoC interface for McBSP sidetone
arch/arm/mach-omap2/mcbsp.c | 2 + arch/arm/plat-omap/include/plat/mcbsp.h | 63 +++++ arch/arm/plat-omap/mcbsp.c | 402 ++++++++++++++++++++++++++++++- sound/soc/omap/omap-mcbsp.c | 187 ++++++++++++++ sound/soc/omap/omap-mcbsp.h | 2 + 5 files changed, 655 insertions(+), 1 deletions(-)