Mike Looijmans wrote:
Some codec registers need negative values. For example, sound/soc/codecs/tlv320aic32x4.c specifies this:
78 SOC_DOUBLE_R_TLV("PCM Playback Volume", AIC32X4_LDACVOL, 79 AIC32X4_RDACVOL, 0, 0x30, 0, tlv_step_0_5),
It's incomplete. The actual range is from -63.5dB to +24dB in 0.5 dB steps. The 8-bit value is interpreted as a signed 8-bit integer, so to get -3dB the register value must be -6 or 0xFA.
How do I explain that to Alsa?
There are some ASoC helper macros that handle signed register fields, such as SOC_DOUBLE_S8_TLV and SOC_SINGLE_XR_SX. If those don't do what you want, you have to write your own.
(and on a side note "amixer" doesn't accept negative values either)
A workaround would be to set the control value first to 0 and then to the desired negative value ... but this bug needs fixing.
Regards, Clemens