[Letux-kernel] FM Sound

H. Nikolaus Schaller hns at goldelico.com
Fri Nov 16 10:03:32 CET 2018

> Am 15.11.2018 um 13:08 schrieb Andreas Kemnade <andreas at kemnade.info>:
> Hi,
> On Thu, 15 Nov 2018 09:20:37 +0100
> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>> 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:
> Well it worked at least with 3.7
>> * pinmux may remain active, but the Si47xx is connected through high value resistors. So there can't be any big leakage current.
> Pinmux is already set by uboot. And not changed by modprobe

I haven't checked everything but

modprobe snd_soc_omap_mcbsp

scans the DT and there is IMHO a reference to the mcbsp node which itself references pinmux and sysconf DT entries.
But they should have been applied during early boot.

>> * 32kHz - maybe it becomes enabled for the first time but it is used for the WLAN module as well and the DM3730 itself
> How should it be enabled then? The si47xx driver almost contains nothing.

Yes, there is no ref to the 32kHz clock.

>> * 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?
> I was not recording/playing anything, so why should any pcm clock be enabled?


> I did not run the power up command, just the modprobe.
> And it worked some time in the past without any quirks.
> I will compare with Letux3704 (no si4721 chip installed)
> Regards,
> Andreas
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