[PATCH] ASoC: tlv320adc3xxx: Add IIR filter configuration

[Mark Brown]

On Wed, Feb 09, 2022 at 06:20:00PM +0100, Ricard Wanderlof wrote:

> In this case it was the ADAU1761 driver and it was several years ago
> and I don't know if it still is an issue. Basically the sequence was 
> something like:

> - System boots up.
> - Codec is configured (I think it was the sample rate, but it could have 
>   been the format or some other I2S parameter) to something that is non 
>   default.
> - System reboots. Since the codec has no means of getting reset, it
>   retains all its register values.
> - This time, an attempt is made to configure the codec with the default
>   sample rate. Since the driver believes the default is already set
>   it does not attempt to write anything, although looking at 
>   regmap_write() now I'm not sure how this could be the case.

update_bits() could also trigger this if it thinks the value didn't
change, but that's at a higher level before it ever gets as far as
trying to do the write and unrelated to the cache (it will also
suppress redundant writes with no cache present).

> - When codec is started, the sample rate / format / whatever is wrong
>   compared to what was allegedly set up.

> It was all rather academic, because the above sequence only occurred in 
> the lab under manual control; in the actual production code the same 
> format and sample rate was used every time, so it wasn't an issue that was 
> pressing to fix. It could as you said have been a bug somewhere else. I 
> distinctly remember the last point about the codec running in seemingly 
> the wrong mode after a (power-cycle-less) reboot at any rate.

A soft reboot could trigger something like that, the easiest fix would
just be to not specify any register defaults so that there's no default
values to compare with.
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