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SubjectRe: [PATCH] ALSA: usb-audio: Fix the mixer control range limiting issue
On Wed, 21 Aug 2019 12:02:25 +0200,
Srinivas Kandagatla wrote:
>
> From: Deepa Madiregama <dmadireg@codeaurora.org>
>
> - mixer_ctl_set() function is limiting the volume level
> to particular range. This results in incorrect initial
> volume setting for that device.
> - In USB mixer while calculating the dBmin/dBmax values
> resolution factor is hardcoded to 256 which results in
> populating the wrong values for dBmin/dBmax.
> - Fix is to use appropriate resolution factor while
> calculating the dBmin/dBmax values.

This change doesn't sound right. Basically the values returned from
USB-audio FEATURE UNIT or MIXER UNIT are always in 1/256 dB unit, per
definition. And we pass dB min/max to user-space as TLV_DB_MINMAX(),
i.e. TLV points just both min and max, no matter what scale is. I
believe that the current code is correct in this regard.

So, it's either a firmware bug that gives the wrong values back, or
the case we still don't cover, e.g. multiple RANGE values for
UAC2/UAC3.

Please check what exactly doesn't work as expected. Which value is
returned from the USB-audio device and what is wrongly interpreted.


thanks,

Takashi


> Signed-off-by: Deepa Madiregama <dmadireg@codeaurora.org>
> Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
> Signed-off-by: Meng Wang <mwang@codeaurora.org>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
> ---
> sound/usb/mixer.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index 5070a6a76ab3..a67448327d07 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -1248,8 +1248,10 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
> /* USB descriptions contain the dB scale in 1/256 dB unit
> * while ALSA TLV contains in 1/100 dB unit
> */
> - cval->dBmin = (convert_signed_value(cval, cval->min) * 100) / 256;
> - cval->dBmax = (convert_signed_value(cval, cval->max) * 100) / 256;
> + cval->dBmin =
> + (convert_signed_value(cval, cval->min) * 100) / (cval->res);
> + cval->dBmax =
> + (convert_signed_value(cval, cval->max) * 100) / (cval->res);
> if (cval->dBmin > cval->dBmax) {
> /* something is wrong; assume it's either from/to 0dB */
> if (cval->dBmin < 0)
> --
> 2.21.0
>

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