[Letux-kernel] FM Sound

Andreas Kemnade andreas at kemnade.info
Fri Nov 16 13:26:51 CET 2018


Hi,

On Fri, 16 Nov 2018 10:03:32 +0100
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:

> > 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.
> 
well, if dt matches what is already set by uboot there will be
no change.

> >   
> >> * 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?  
> 
> Default?
> 

I would rule that out. But powering on the shortly 
mcbsp by userspace or during probe might change the status of these line.
So the next step would be to play around with some mode 7 settings
of the corresponding pins.

Regards,
Andreas
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