struct mychip {
          ....
          struct snd_ac97 *ac97;
          ....
  };

  static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
                                             unsigned short reg)
  {
          struct mychip *chip = ac97->private_data;
          ....
          /* read a register value here from the codec */
          return the_register_value;
  }

  static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
                                   unsigned short reg, unsigned short val)
  {
          struct mychip *chip = ac97->private_data;
          ....
          /* write the given register value to the codec */
  }

  static int snd_mychip_ac97(struct mychip *chip)
  {
          struct snd_ac97_bus *bus;
          struct snd_ac97_template ac97;
          int err;
          static struct snd_ac97_bus_ops ops = {
                  .write = snd_mychip_ac97_write,
                  .read = snd_mychip_ac97_read,
          };

          err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
          if (err < 0)
                  return err;
          memset(&ac97, 0, sizeof(ac97));
          ac97.private_data = chip;
          return snd_ac97_mixer(bus, &ac97, &chip->ac97);
  }