[RFC PATCH 02/16] ASoC: pcm512x: use "sclk" string to retrieve clock

[Pierre-Louis Bossart]

On 4/15/20 4:52 AM, Andy Shevchenko wrote:
> On Tue, Apr 14, 2020 at 12:54:25PM -0500, Pierre-Louis Bossart wrote:
>> On 4/14/20 12:11 PM, Andy Shevchenko wrote:
>>> On Thu, Apr 09, 2020 at 02:58:27PM -0500, Pierre-Louis Bossart wrote:
>>>> Using devm_clk_get() with a NULL string fails on ACPI platforms, use
>>>> the "sclk" string as a fallback.
>>>
>>> This is fishy a bit.
>>
>> I didn't find a single example where we use a NULL string in ACPI cases?
> 
> ...
> 
>>> If no, why not simple switch to devm_clk_get_optional()?
>>
>> Not sure what that would change?
> 
> Hmm... Who is the provider of this clock?

Well, at the hardware level, the clock is provided by two local 
oscillators controlled by the codec GPIOs. So you could consider that 
the codec is both the provider and consumer of the clock.

In the Linux world, the PCM512x codec driver creates a gpiochip. And the 
clk driver uses the gpios to expose a clk used by the PCM512x codec driver.

I am not fully happy with this design because it creates a double 
dependency which makes it impossible to remove modules. But I don't know 
how to model it otherwise.

But to go back to your question, the two parts are really joined at the 
hip since the same gpios exposed by one is used by the other.