[PATCH] ALSA: usb-audio: Fix the mixer control range limiting issue

[PATCH] ALSA: usb-audio: Fix the mixer control range limiting issue

[Srinivas Kandagatla]

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.

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

Re: [PATCH] ALSA: usb-audio: Fix the mixer control range limiting issue

[Takashi Iwai]

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
> 

Re: [PATCH] ALSA: usb-audio: Fix the mixer control range limiting issue

[Srinivas Kandagatla]

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
>>