ASoC: core: Add signed register volume control logic

Some codecs use signed volume control representation with non standard
register sizes, e.g. 6 or 7 bit signed integers.

This patch adds generic signed register volume control logic to
soc-core. Instead of a fixed width signed register control, this
implementation uses a 'min' value and the signed bit location to translate
it to an absolute volume. Using the 'sign_bit' we can calculate a
correct mask for the register values and translate it back into signed
integers of standard size.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Mark Brown <broonie@linaro.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/sound/soc.h b/include/sound/soc.h
index 9a001472b96a..a25f3ccb3fde 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -1067,6 +1067,7 @@ struct soc_mixer_control {
 	int min, max, platform_max;
 	int reg, rreg;
 	unsigned int shift, rshift;
+	unsigned int sign_bit;
 	unsigned int invert:1;
 	unsigned int autodisable:1;
 };