struct audio_stream_cmd_set_gain_req

AUDIO_STREAM_CMD_SET_GAIN

Request that a stream change its gain settings to most closely match those

requested. Gain values for Valid requests will be rounded to the nearest

gain step. For example, if a stream can control its gain on the range from

-60.0 to 0.0 dB, a request to set the gain to -33.3 dB will result in a gain

of -33.5 being applied.

Gain change requests outside of the capabilities of the stream's

amplifier will be rejected with a result of ZX_ERR_INVALID_ARGS. Using the

previous example, requests for gains of -65.0 or +3dB would be rejected.

Similarly, If an amplifier is capable of gain control but cannot mute, a

request to mute will be rejected.

TODO(johngro) : Is this the correct behavior? Should we just apply sensible

limits instead? IOW - If the user requests a gain of -1000 dB, should we

just set the gain to -60dB? Likewise, if they request mute but the amplifier

has no hard mute feature, should we just set the gain to the minimum

permitted gain?

May be used with the NO_ACK flag.