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## Metadata

To provide information about the dB values of a mixer control, use on of the `DECLARE_TLV_xxx` macros from `<sound/tlv.h>` to define a variable containing this information, set the`tlv.p` field to point to this variable, and include the `SNDRV_CTL_ELEM_ACCESS_TLV_READ` flag in the `access` field; like this:

      static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);

      static struct snd_kcontrol_new my_control = {
              ...
              .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
                        SNDRV_CTL_ELEM_ACCESS_TLV_READ,
              ...
              .tlv.p = db_scale_my_control,
      };

The `DECLARE_TLV_DB_SCALE` macro defines information about a mixer control where each step in the control's value changes the dB value by a constant dB amount. The first parameter is the name of the variable to be defined. The second parameter is the minimum value, in units of 0.01 dB. The third parameter is the step size, in units of 0.01 dB. Set the fourth parameter to 1 if the minimum value actually mutes the control.

The `DECLARE_TLV_DB_LINEAR` macro defines information about a mixer control where the control's value affects the output linearly. The first parameter is the name of the variable to be defined. The second parameter is the minimum value, in units of 0.01 dB. The third parameter is the maximum value, in units of 0.01 dB. If the minimum value mutes the control, set the second parameter to `TLV_DB_GAIN_MUTE`.

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