PCM_VOLCH
volch = PCM_VOLCH(dev);
ret = dsp_ioctl_channel(i_dev, PCM_VOLCH(i_dev), cmd, arg);
PCM_VOLCH(dev) == NULL,
volch = PCM_VOLCH(i_dev);
PCM_VOLCH(i_dev) = NULL;
c = PCM_VOLCH(dev);
PCM_VOLCH(dev) = c;