[alsa-devel] [PATCH] sound/usb: add dB range mapping quirks.

[Takashi Iwai]

On Tue, 28 Jul 2015 10:06:45 +0200,
Yao-Wen Mao wrote:
> 
> Some usb audio devices don't follow the specification of the
> volume range. Add dB_mapping_quirks to fix some devices' dB
> ranges so that the function snd_mixer_selem_set_playback_dB in
> alsa-lib can set the correct value for those devices.
> 
> Signed-off-by: Yao-Wen Mao <yaowen at google.com>

This can be done also by adding to mixer_maps.c.
The map doesn't have to contain the name string but only with a dB
entry (I think).

OTOH, this patch shows the value factor to be corrected, so it may
make more sense -- people can look at these as a reference.

One thing I wonder, though: can it be simplified by introducing the dB
conversion factor instead?  Do these devices have other FUs that have
a different volume factor?


thanks,

Takashi

> ---
>  sound/usb/mixer.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index 6b3acba..b6b27dc 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -933,6 +933,32 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
>  	}
>  }
>  
> +/* dB mapping quirks */
> +static void dB_mapping_quirks(struct usb_mixer_elem_info *cval,
> +			      struct snd_kcontrol *kctl)
> +{
> +	switch (cval->mixer->chip->usb_id) {
> +	case USB_ID(0x05a7, 0x1020): /* Bose Companion 5 */
> +		if (strcmp(kctl->id.name, "PCM Playback Volume") == 0) {
> +			cval->dBmin = (convert_signed_value(cval, cval->min) * 100) / 16;
> +			cval->dBmax = (convert_signed_value(cval, cval->max) * 100) / 16;
> +		}
> +		break;
> +	case USB_ID(0x21b4, 0x0081): /* Dragonfly DAC 1.2 */
> +		if (strcmp(kctl->id.name, "PCM Playback Volume") == 0) {
> +			cval->dBmin = convert_signed_value(cval, cval->min) * 100;
> +			cval->dBmax = convert_signed_value(cval, cval->max) * 100;
> +		}
> +		break;
> +	case USB_ID(0x046d, 0x0a29): /* Logitech H800 */
> +		if (strcmp(kctl->id.name, "PCM Playback Volume") == 0) {
> +			cval->dBmin = convert_signed_value(cval, cval->min);
> +			cval->dBmax = convert_signed_value(cval, cval->max);
> +		}
> +		break;
> +	}
> +}
> +
>  /*
>   * retrieve the minimum and maximum values for the specified control
>   */
> @@ -1027,6 +1053,10 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
>  	 */
>  	cval->dBmin = (convert_signed_value(cval, cval->min) * 100) / 256;
>  	cval->dBmax = (convert_signed_value(cval, cval->max) * 100) / 256;
> +
> +	if (kctl)
> +		dB_mapping_quirks(cval, kctl);
> +
>  	if (cval->dBmin > cval->dBmax) {
>  		/* something is wrong; assume it's either from/to 0dB */
>  		if (cval->dBmin < 0)
> -- 
> 2.5.0.rc2.392.g76e840b
> 
>