Re: [PATCH] ASoC: pcm512x: Mend accesses to the I2S_1 and I2S_2 registers

[Peter Rosin <peda@axentia.se>]

On 2021-09-20 23:29, Mark Brown wrote:
> On Mon, Sep 20, 2021 at 09:37:37PM +0200, Peter Rosin wrote:
> 
>> compare if the update was needed at all. But marking volatile wasn't
>> enough. I also tried to set both a default and mark as volatile,
>> but it seems every read fails with -16 (EBUSY). I don't get why, to me
>> it almost feels like a regmap issue of some sort (probably the regmap
>> config is bad in some way), but I'm not fluent in regmap...
> 
> Having a default for a volatile register isn't really a sensible
> configuration since the whole point with volatile registers is
> that they change underneath us, I'd not be surprised if we had
> some error checking code in there that was trying to tell you
> there was a problem though it does seem like it should at least
> be more verbose about it since returning -EBUSY isn't exactly
> helpful by itself.

I totally agree that it's not a sensible config to set up a register
with a default when it's marked as volatile. That was just a wild
attempt.

I expected it to just work to mark the register as readable and do
without the default value (i.e. the way it was before my patch). What
I don't understand is why regmap returns -EBUSY in that case. That
doesn't make sense to me. Perhaps that -EBUSY is propagated from the
I2C layer, but in that case, why is it then ok to do a write to
another register at the same spot in the code? So, why -EBUSY?

Something is going on that is not understood. At least not by me.

Cheers,
Peter