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SubjectRe: [PATCH] ALSA: usb-audio: Fix the mixer control range limiting issue
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On 21/08/2019 18:05, Takashi Iwai wrote:
> 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 for the detailed review.

I see https://www.usb.org/sites/default/files/audio10.pdf clearly
specifies Mixer unit is always 1/256dB units.

This patch has been carried in Qcom downstream kernels for past many
years to fix very low Initial volume setting on some USB headsets like
Logitech S-150 USB Speakers and Nokia HS-82 USB headset.

Its highly likely that its a firmware bug!, but I will try to get it
retested on latest kernel and collect some logs!

Thanks,
srini


>
> 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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