Re: [PATCH v3 2/2] ASoC: cs530x: Support for cs530x ADCs

[Richard Fitzgerald <rf@opensource.cirrus.com>]

On 18/06/2024 15:25, Mark Brown wrote:
> On Tue, Jun 18, 2024 at 03:23:07PM +0100, Richard Fitzgerald wrote:
>> On 18/06/2024 15:18, Mark Brown wrote:
>>> On Mon, Jun 17, 2024 at 02:01:02PM -0500, Paul Handrigan wrote:
> 
>>>> +	case CS530X_DEVID:
>>>> +	case CS530X_REVID:
> 
>>> Are these really volatile?  I would expect them to have no defaults so
>>> they must be read from the device, but once read I'd expect we could
>>> cache the values.
> 
>> If you mark a register non-volatile but without default, a
>> regcache_sync() will write it back out to the device. While that
>> doesn't necessarily do any harm, that depends on what these
>> registers do on write. Generally it makes me nervous to have
>> cache syncs writing to registers we don't want to write to.
> 
> Marking the register as read only should DTRT there, if not then that's
> a regmap bug which should be fixed.

True but now we're adding extra callbacks and complexity just to
avoid marking a register volatile for some reason. The driver doesn't
need it to be cached, so why bother?