[PATCH 2/4] soundwire: Provide build stubs for common functions

[Pierre-Louis Bossart]

On 11/15/22 05:41, Richard Fitzgerald wrote:
> On 15/11/2022 11:03, Charles Keepax wrote:
>> On Mon, Nov 14, 2022 at 10:13:07AM -0600, Pierre-Louis Bossart wrote:
>>>
>>>
>>> On 11/14/22 04:29, Charles Keepax wrote:
>>>> Provide stub functions when CONFIG_SOUNDWIRE is not set for functions
>>>> that are quite likely to be used from common code on devices supporting
>>>> multiple control buses.
>>>
>>> So far this case has been covered by splitting SoundWire related code
>>> away from, say I2C, and with a clear 'depends on SOUNDWIRE'. This is the
>>> case for rt5682, max98373, etc.
>>>
>>> Is this not good enough?
>>>
>>> I am not against this patch, just wondering if allowing code for
>>> different interfaces to be part of the same file will lead to confusions
>>> with e.g. register offsets or functionality exposed with different
>>> registers.
>>>
>>
>> I guess this is a bit of a grey area this one. Both work, I guess
>> the reason I was leaning this way is that in order to avoid a
>> circular dependency if I put all the soundwire DAI handling into
>> the soundwire code then I have to duplicate the snd_soc_dai_driver
>> structure into both the sdw and i2c specific code (worth noting
>> the I2S DAIs are still usable when the part is sdw to the host). But
>> there are also downsides to this approach in that it will likely have
>> some small impact on driver size when soundwire is not built in.
>>
> 
> I think we should just add the stubs. Other subsystems use stubs to help
> with code that references stuff that might not be available.
> 
> Splitting all the soundwire-specifics out into a separate module works
> for simple chips that are either I2S or soundwire. but can get messy for
> a complex codec. I used the separate file method for CS42L42, but for a
> driver I'm working on I abandoned that and put both DAIs in the core
> code. I didn't notice the missing stubs because my defconfig that was
> intended to omit soundwire apparently has something that is selecting
> it anyway.

It would be good if you could look into this, I don't see any 'select
SOUNDWIRE'.

I agree the premise of the split was that the device is used in one mode
of the other, I am not sure however what the a 'complex codec' would
change. It's likely that we will see a second level within a SoundWire
device to deal with independent 'functions', but I don't quite see how
this would matter.

That said, I don't write codec drivers so I am not going to lay on the
tracks over 2 stubs. We can revisit the sdw.h split as well later.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>