[alsa-devel] ADAU1761 default register value problem

[Ricard Wanderlof]

On Fri, 13 May 2016, Lars-Peter Clausen wrote:

> > Having researched this further, it appears that commit
> > 
> > 27d6e7d1c96c9f51379e0feb972fec26029098bc
> > 
> > ASoC: adau17x1: Cache writes when core clock is disabled
> 
> I think it is also related to commit 1c79771a7270 ("regmap: Use
> regcache_mark_dirty() to indicate power loss or reset"). This changes the
> regmap code to sync all registers under certain conditions.

Yes, that commit seems to be the key, although I must admit that I can't 
get my head around the logic of that commit. The commit message says: "HW 
was not reset (maybe it was just clock-gated), so if we cached any writes, 
they should be sent to the hardware regardless of whether they match the 
HW default.". But if the device was indeed gated off, rather than reset, 
why should this make a difference when writing out the cache after gating 
the chip on again? If it were gated off and then on, doesn't this imply 
that the register settings won't change? Or is the idea that the chip 
might loose all its state while gated off and hence essentially needs to 
be reinitialized?

Regardless of the commit message, the code indeed does cause all the 
cached data to be written out when regcache_sync() is called in this case.

> We still have the issue though that the CODEC is in an undefined state until
> the first OFF to STANDBY transitions happens. Usually this will happen early
> on when the CODEC is bound to the sound card, but if it is not bound
> immediately it might stay there for a bit longer. So depending on the setup
> this may or may not be a problem.

So that means that in the probe function we should really write out the 
default values, by enabling SYSCLK_EN in the ADAU clock control register, 
and then calling regcache_sync() before disabling SYSCLK_EN again, and 
going to regcache_cache_only(..,true) ?

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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