[Letux-kernel] FM Sound

[H. Nikolaus Schaller]

Hi,

> Am 15.11.2018 um 07:28 schrieb Andreas Kemnade <andreas at kemnade.info>:
> 
> Hi,
> 
> some analysis about fm sound:
> 
> starting with no sound modules loaded
> 
> and then loading this:
> snd_soc_simple_card
> snd_soc_omap_mcbsp
> snd_soc_si47xx
> 
> increases idle current by 10mA
> I have also seen increased suspend current by 10mA
> 
> rmmod does not reset these things back to normal. With 4.19.

I have checked some more ideas:

* pinmux may remain active, but the Si47xx is connected through high value resistors. So there can't be any big leakage current.
* 32kHz - maybe it becomes enabled for the first time but it is used for the WLAN module as well and the DM3730 itself
* something inside the si47xx stays in reset state until PCM clocks are applied first and then it is up and running - so it may need a "shutdown" through I2C
  Looking into AN319 shows that there are explicit POWER_UP and POWER_DOWN commands
  So we might have to run ./si4721 -dn before removing the driver?

BR,
Nikolaus