Re: [PATCH] ASoC: soc-ops: Correct the max value for clamp in soc_mixer_reg_to_ctl()

["Péter Ujfalusi" <peter.ujfalusi@linux.intel.com>]

On 17/12/2025 14:47, Charles Keepax wrote:
> On Wed, Dec 17, 2025 at 02:06:23PM +0200, Peter Ujfalusi wrote:
>>  sound/soc/soc-ops.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/sound/soc/soc-ops.c b/sound/soc/soc-ops.c
>> index ce86978c158d..6a18c56a9746 100644
>> --- a/sound/soc/soc-ops.c
>> +++ b/sound/soc/soc-ops.c
>> @@ -148,7 +148,7 @@ static int soc_mixer_reg_to_ctl(struct soc_mixer_control *mc, unsigned int reg_v
>>  	if (mc->sign_bit)
>>  		val = sign_extend32(val, mc->sign_bit);
>>  
>> -	val = clamp(val, mc->min, mc->max);
>> +	val = clamp(val, mc->min, mc->min + max);
> 
> This won't work, for an SX control it is perfectly valid for
> the value read from the register to be smaller than the minimum
> value specified in the control.

Hrm, so an SX control returns sort of rand() and the value have no
correlation to min or max?

The info() gives this explanation:
SX TLV controls have a range that represents both positive and negative
values either side of zero but without a sign bit. min is the minimum
register value, max is the number of steps.

which kind of makes some sense, but really fuzzy.
> The minimum value gives the register value that equates to the
> smallest possible control value.

right, so min is min, OK

> From there the values increase
> but the register field can overflow and end up lower than the
> min.

smaller value than min is then bigger than min, right?
The value can wrap at any random value to 0 and continue from 0 up to
some value, which is the max?
max (which is the number of steps) = vrap_point-min + some_value (where
the value is likely less than min, but not specified)

How this is in practice for the cs42l43' Headphone Digital Volume?
SOC_DOUBLE_SX_TLV("Headphone Digital Volume", CS42L43_HPPATHVOL,
	  CS42L43_AMP3_PATH_VOL_SHIFT, CS42L43_AMP4_PATH_VOL_SHIFT,
	  0x11B, 229, cs42l43_headphone_tlv),

min=283
max=229
shifts: 0 and 16
masks are 0x1ff

if you step 229 from 283 then you reach 0x1ff, this is the max the mask
can cover.

> I often think of it in terms of a 2's compliement number
> with an implicit sign bit.

I see, but why???

> 
> Thanks,
> Charles

-- 
Péter