Re: [PATCH] ASoC: ops: Fix the bounds checking in snd_soc_put_volsw_sx and snd_soc_put_xr_sx

["Tan Nayır" <tannayir@gmail.com>]

 > No, the minimum value we expose to userspace is always scaled so that
 > userspace sees a range starting from zero and that's where platform_max
 > is referenced to - we're applying this limit before we start remapping
 > to actual register values. The code would be a lot simpler if we didn't
 > do this rescaling.

These are the results that I got from debugging my phone
which has a wcd9340 audio codec and a kernel version of 4.9.314:
The control is defined like
-- SOC_SINGLE_S8_TLV("IIR0 INP0 Volume", 
WCD934X_CDC_SIDETONE_IIR0_IIR_GAIN_B1_CTL, -84, 40, digital_gain) --

Now the OEM mixer_path.xml file defines the value of the aforementioned 
control as 54
which is read by the user-mode Qualcomm HAL, the HAL then uses the 
library libalsa-intf
to issue an IOCTL to pass this value directly to the ALSA driver.
At this point, the snd_soc_put_volsw_sx is called and the $val is 54 as 
expected.
$mc->platform_max is 40, $mc->max is also 40 and $mc->min is -84.

The problem is that the snd_soc_put_volsw_sx, checks the userspace value 
that has a range
starting from 0, directly against the $mc->platform_max value mentioned 
above
which is set to 40 at that point so it checks for the incorrect range.