[alsa-devel] [PATCH 1/2 v5] ALSA: usb-audio: Add mixer control for Digidesign mbox 1 clock source

[Takashi Iwai]

At Mon, 10 Nov 2014 21:17:54 +1100,
Damien Zammit wrote:
> +static int snd_mbox1_switch_get(struct snd_kcontrol *kctl,
> +				struct snd_ctl_elem_value *ucontrol)
> +{
> +	if (kctl->private_value) {
> +		ucontrol->value.enumerated.item[0] = true;
> +		return 0;
> +	}
> +
> +	ucontrol->value.enumerated.item[0] = false;

A simpler code would be just like:

	ucontrol->value.enumerated.item[0] = kctl->private_value;
	return 0;

> +	return 0;
> +}
> +
> +static int snd_mbox1_switch_put(struct snd_kcontrol *kctl,
> +				struct snd_ctl_elem_value *ucontrol)
> +{
> +	struct snd_usb_audio *chip;
> +	struct usb_mixer_interface *mixer;
> +	int err;
> +	bool changed, cur_val, new_val;
> +	bool value;

I guess this "value" variable can be dropped completely?

> +	unsigned char buff[3];
> +
> +	changed = false;
> +	value = false;
> +
> +	cur_val = kctl->private_value;
> +	new_val = ucontrol->value.enumerated.item[0];
> +
> +	mixer = snd_kcontrol_chip(kctl);
> +	if (snd_BUG_ON(!mixer))
> +		return -EINVAL;
> +
> +	chip = mixer->chip;
> +	if (snd_BUG_ON(!chip))
> +		return -EINVAL;
> +
> +	/* update value if needed */
> +	if (cur_val != new_val) {
> +		value = new_val;
> +		down_read(&chip->shutdown_rwsem);
> +		if (chip->shutdown) {
> +			err = -ENODEV;
> +			goto err;
> +		} else {
> +			/* Prepare for magic command to toggle clock source */
> +			err = snd_usb_ctl_msg(chip->dev,
> +				usb_rcvctrlpipe(chip->dev, 0), 0x81,
> +				USB_DIR_IN |
> +				USB_TYPE_CLASS |
> +				USB_RECIP_INTERFACE, 0x00, 0x500, buff, 1);
> +			if (err < 0)
> +				goto err;
> +			err = snd_usb_ctl_msg(chip->dev,
> +				usb_rcvctrlpipe(chip->dev, 0), 0x81,
> +				USB_DIR_IN |
> +				USB_TYPE_CLASS |
> +				USB_RECIP_ENDPOINT, 0x100, 0x81, buff, 3);
> +			if (err < 0)
> +				goto err;
> +			/* 2 possibilities:	Internal    -> send sample rate
> +			 *			S/PDIF sync -> send zeroes
> +			 * NB: Sample rate locked to 48kHz on purpose to
> +			 *     prevent user from resetting the sample rate
> +			 *     while S/PDIF sync is enabled and confusing
> +			 *     this configuration.
> +			 */
> +			if (new_val == 0) {
> +				buff[0] = 0x80;
> +				buff[1] = 0xbb;
> +				buff[2] = 0x00;
> +			} else {
> +				buff[0] = buff[1] = buff[2] = 0x00;
> +			}
> +			/* Send the magic command to toggle the clock source */
> +			err = snd_usb_ctl_msg(chip->dev,
> +				usb_sndctrlpipe(chip->dev, 0), 0x1,
> +				USB_TYPE_CLASS |
> +				USB_RECIP_ENDPOINT, 0x100, 0x81, buff, 3);
> +			if (err < 0)
> +				goto err;
> +			err = snd_usb_ctl_msg(chip->dev,
> +				usb_rcvctrlpipe(chip->dev, 0), 0x81,
> +				USB_DIR_IN |
> +				USB_TYPE_CLASS |
> +				USB_RECIP_ENDPOINT, 0x100, 0x81, buff, 3);
> +			if (err < 0)
> +				goto err;
> +			err = snd_usb_ctl_msg(chip->dev,
> +				usb_rcvctrlpipe(chip->dev, 0), 0x81,
> +				USB_DIR_IN |
> +				USB_TYPE_CLASS |
> +				USB_RECIP_ENDPOINT, 0x100, 0x2, buff, 3);
> +			if (err < 0)
> +				goto err;
> +		}
> +		up_read(&chip->shutdown_rwsem);
> +		kctl->private_value = new_val;
> +		changed = true;
> +	}
> +
> +	return changed;
> +err:
> +	up_read(&chip->shutdown_rwsem);
> +	return err;

A bit better way would be something like:

	if (cur_val == new_val)
		return 0;

	down_read(&chip->shutdown_rwsem);
	if (chip->shutdown) {
		err = -ENODEV;
		goto err;
	}

	/* Prepare for magic command to toggle clock source */
	err = snd_usb_ctl_msg(chip->dev,
				usb_rcvctrlpipe(chip->dev, 0), 0x81,
				USB_DIR_IN |
				USB_TYPE_CLASS |
				USB_RECIP_INTERFACE, 0x00, 0x500, buff, 1);
	if (err < 0)
		goto err;
	....

	kctl->private_value = new_val;

err:
	up_read(&chip->shutdown_rwsem);
	return err < 0 ? err : 1;
}


This flattens the flow and combines the unlock in a single place.
Also, "changed" variable can be dropped in this way.


Takashi