[PATCH] ASoC: tlv320adc3xxx: Add IIR filter configuration

[Mark Brown]

On Wed, Feb 09, 2022 at 03:53:28PM +0100, Ricard Wanderlof wrote:
> On Tue, 8 Feb 2022, Mark Brown wrote:
> > On Mon, Feb 07, 2022 at 06:12:06PM +0100, Ricard Wanderlof wrote:

> > Other than resyncing the cache (and see below for that) a cache will
> > affect reads not writes, writes should be affected unless the driver
> > turns on cache only mode.

> Isn't one consequence of caching that writing to a register which is known 
> to already have the value to be written are simply skipped? 

No, look at the code for regmap_write().

> I remember having that problem with a codec which did not have any means 
> of resetting the codec other than power-on-reset (i.e. no reset pin or 
> software controlled reset). If the system was rebooted without cycling the 
> power, the registers would potentially contain non-default values, and 
> this meant that for instance attempting to explicitly set the sample rate 
> to the default value was not possible, as the regcache assumed that the 
> default value was already set and thus skipped the corresponding register 

This is during a cache sync, a sync will only write out non-default
values if the device was flagged as having been reset in order to reduce
power on times.  Your driver is not doing a cache sync at any point so
won't be affected by this, but in any case...

> write. (A workaround was to write another sample rate and then default).

If your driver has no way of ensuring that the device has default
register values your driver should just not specify any register
defaults, but in this case it sounds like you have some other bug going
on.  If the device is getting suspended with a default value set in the
registers then comes out of suspend with a non-default value it's hard
to see how that could happen in the hardware, either the device will
retain the value it had or it will reset to power on default but either
way it's the same value.  I have seen drivers bypassing the cache for a
shutdown sequence that wrote non-default values to the hardware without
updating the cache.
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